How to prove the triangle is isosceles and determine its area
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Let $P(a,b)$ be a point on the curve $y = frac{1}{x}$ in first quadrant and let the tangent line at $P$ intersect the $x$-axis at a point $A$. Show that triangle $AOP$ is isosceles and determine its area, where $O$ is the origin.
How do I start to attempt this?
analytic-geometry plane-geometry
$endgroup$
add a comment |
$begingroup$
Let $P(a,b)$ be a point on the curve $y = frac{1}{x}$ in first quadrant and let the tangent line at $P$ intersect the $x$-axis at a point $A$. Show that triangle $AOP$ is isosceles and determine its area, where $O$ is the origin.
How do I start to attempt this?
analytic-geometry plane-geometry
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1
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Have you tried to find the tangent line in terms of $P$ yet?
$endgroup$
– SmileyCraft
Dec 13 '18 at 14:18
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Very good. So the slope of $PA$ is $-1/a^2$. Now if you also calculate the slope of $OP$ you should notice something which makes the triangle very symmetric.
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– SmileyCraft
Dec 13 '18 at 15:04
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So essentially, the slope of $OP$ is just the inverse of $PA$? @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:10
$begingroup$
Right, the additive inverse that is. Because $O$ and $A$ lie on the $x$-axis, it follows that $|PA|$=$|OP|$.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:12
$begingroup$
I see now. Thank you so much for your assistance! @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:13
add a comment |
$begingroup$
Let $P(a,b)$ be a point on the curve $y = frac{1}{x}$ in first quadrant and let the tangent line at $P$ intersect the $x$-axis at a point $A$. Show that triangle $AOP$ is isosceles and determine its area, where $O$ is the origin.
How do I start to attempt this?
analytic-geometry plane-geometry
$endgroup$
Let $P(a,b)$ be a point on the curve $y = frac{1}{x}$ in first quadrant and let the tangent line at $P$ intersect the $x$-axis at a point $A$. Show that triangle $AOP$ is isosceles and determine its area, where $O$ is the origin.
How do I start to attempt this?
analytic-geometry plane-geometry
analytic-geometry plane-geometry
edited Dec 14 '18 at 14:05
amWhy
1
1
asked Dec 13 '18 at 14:14
Valèt QuasarValèt Quasar
32
32
1
$begingroup$
Have you tried to find the tangent line in terms of $P$ yet?
$endgroup$
– SmileyCraft
Dec 13 '18 at 14:18
$begingroup$
Very good. So the slope of $PA$ is $-1/a^2$. Now if you also calculate the slope of $OP$ you should notice something which makes the triangle very symmetric.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:04
$begingroup$
So essentially, the slope of $OP$ is just the inverse of $PA$? @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:10
$begingroup$
Right, the additive inverse that is. Because $O$ and $A$ lie on the $x$-axis, it follows that $|PA|$=$|OP|$.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:12
$begingroup$
I see now. Thank you so much for your assistance! @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:13
add a comment |
1
$begingroup$
Have you tried to find the tangent line in terms of $P$ yet?
$endgroup$
– SmileyCraft
Dec 13 '18 at 14:18
$begingroup$
Very good. So the slope of $PA$ is $-1/a^2$. Now if you also calculate the slope of $OP$ you should notice something which makes the triangle very symmetric.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:04
$begingroup$
So essentially, the slope of $OP$ is just the inverse of $PA$? @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:10
$begingroup$
Right, the additive inverse that is. Because $O$ and $A$ lie on the $x$-axis, it follows that $|PA|$=$|OP|$.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:12
$begingroup$
I see now. Thank you so much for your assistance! @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:13
1
1
$begingroup$
Have you tried to find the tangent line in terms of $P$ yet?
$endgroup$
– SmileyCraft
Dec 13 '18 at 14:18
$begingroup$
Have you tried to find the tangent line in terms of $P$ yet?
$endgroup$
– SmileyCraft
Dec 13 '18 at 14:18
$begingroup$
Very good. So the slope of $PA$ is $-1/a^2$. Now if you also calculate the slope of $OP$ you should notice something which makes the triangle very symmetric.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:04
$begingroup$
Very good. So the slope of $PA$ is $-1/a^2$. Now if you also calculate the slope of $OP$ you should notice something which makes the triangle very symmetric.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:04
$begingroup$
So essentially, the slope of $OP$ is just the inverse of $PA$? @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:10
$begingroup$
So essentially, the slope of $OP$ is just the inverse of $PA$? @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:10
$begingroup$
Right, the additive inverse that is. Because $O$ and $A$ lie on the $x$-axis, it follows that $|PA|$=$|OP|$.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:12
$begingroup$
Right, the additive inverse that is. Because $O$ and $A$ lie on the $x$-axis, it follows that $|PA|$=$|OP|$.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:12
$begingroup$
I see now. Thank you so much for your assistance! @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:13
$begingroup$
I see now. Thank you so much for your assistance! @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:13
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
To start approaching the problem, first notice that if P lies on the curve then $P (a, b) = P (a, frac{1}{a})$.
Secondly, find the slope of the tangent line at $P$, which is precisely $-frac{1}{a^2}$
Thus equation of the tangent line through $P$ is given by
$$(y - frac{1}{a}) = (-frac{1}{a^2})(x-a) implies a^2y = 2a - x$$
The above line intersects the $x$-axis only at $(2a, 0)$, thus $ A = (2a, 0)$.
Therefore the coordinates of $Delta AOP$ are precisely: $$A (2a, 0), O(0, 0), P (a, frac{1}{a})$$
making $AOP$ isosceles. Moreover, the area of $Delta AOP = frac{1}{2} cdot 2a cdot frac{1}{a} = 1$ unit.
$endgroup$
add a comment |
$begingroup$
Hint:
WLOG $b=1/a>0$
$$xy-1implies xdfrac{dy}{dx}+y=0impliesdfrac{dy}{dx}_{text{ at }(a,b)}=-dfrac{1/a}a=-dfrac1{a^2}$$
The equation of the tangent at $P,$ $$dfrac{y-1/a}{x-a}=-dfrac1{a^2}iff x+a^2y=2a$$
As $x$ axis, $y=0,$ the intersection will be $A(2a,0)$
$$|AP|=?, |OP|=?$$
$endgroup$
add a comment |
$begingroup$
The tangent line to $y=frac 1x$ at $P(x_0,y_0)$ is:
$$y=y_0+y'(x_0)(x-x_0)=frac 1{x_0}-frac 1{x_0^2}(x-x_0).$$
The point $A(x_1,0)$ has coordinate $x_1$:
$$0=frac 1{x_0}-frac 1{x_0^2}(x_1-x_0) Rightarrow x_1=2x_0,$$
which shows the triangle $PAO$ is isosceles, because the altitude $PB$ is the median too.
Now the area of $Delta PAO$ is:
$$S=frac 12 cdot AOcdot PB=frac12 cdot 2x_0 cdot frac1{x_0}=1.$$
$endgroup$
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
To start approaching the problem, first notice that if P lies on the curve then $P (a, b) = P (a, frac{1}{a})$.
Secondly, find the slope of the tangent line at $P$, which is precisely $-frac{1}{a^2}$
Thus equation of the tangent line through $P$ is given by
$$(y - frac{1}{a}) = (-frac{1}{a^2})(x-a) implies a^2y = 2a - x$$
The above line intersects the $x$-axis only at $(2a, 0)$, thus $ A = (2a, 0)$.
Therefore the coordinates of $Delta AOP$ are precisely: $$A (2a, 0), O(0, 0), P (a, frac{1}{a})$$
making $AOP$ isosceles. Moreover, the area of $Delta AOP = frac{1}{2} cdot 2a cdot frac{1}{a} = 1$ unit.
$endgroup$
add a comment |
$begingroup$
To start approaching the problem, first notice that if P lies on the curve then $P (a, b) = P (a, frac{1}{a})$.
Secondly, find the slope of the tangent line at $P$, which is precisely $-frac{1}{a^2}$
Thus equation of the tangent line through $P$ is given by
$$(y - frac{1}{a}) = (-frac{1}{a^2})(x-a) implies a^2y = 2a - x$$
The above line intersects the $x$-axis only at $(2a, 0)$, thus $ A = (2a, 0)$.
Therefore the coordinates of $Delta AOP$ are precisely: $$A (2a, 0), O(0, 0), P (a, frac{1}{a})$$
making $AOP$ isosceles. Moreover, the area of $Delta AOP = frac{1}{2} cdot 2a cdot frac{1}{a} = 1$ unit.
$endgroup$
add a comment |
$begingroup$
To start approaching the problem, first notice that if P lies on the curve then $P (a, b) = P (a, frac{1}{a})$.
Secondly, find the slope of the tangent line at $P$, which is precisely $-frac{1}{a^2}$
Thus equation of the tangent line through $P$ is given by
$$(y - frac{1}{a}) = (-frac{1}{a^2})(x-a) implies a^2y = 2a - x$$
The above line intersects the $x$-axis only at $(2a, 0)$, thus $ A = (2a, 0)$.
Therefore the coordinates of $Delta AOP$ are precisely: $$A (2a, 0), O(0, 0), P (a, frac{1}{a})$$
making $AOP$ isosceles. Moreover, the area of $Delta AOP = frac{1}{2} cdot 2a cdot frac{1}{a} = 1$ unit.
$endgroup$
To start approaching the problem, first notice that if P lies on the curve then $P (a, b) = P (a, frac{1}{a})$.
Secondly, find the slope of the tangent line at $P$, which is precisely $-frac{1}{a^2}$
Thus equation of the tangent line through $P$ is given by
$$(y - frac{1}{a}) = (-frac{1}{a^2})(x-a) implies a^2y = 2a - x$$
The above line intersects the $x$-axis only at $(2a, 0)$, thus $ A = (2a, 0)$.
Therefore the coordinates of $Delta AOP$ are precisely: $$A (2a, 0), O(0, 0), P (a, frac{1}{a})$$
making $AOP$ isosceles. Moreover, the area of $Delta AOP = frac{1}{2} cdot 2a cdot frac{1}{a} = 1$ unit.
edited Dec 14 '18 at 13:54
answered Dec 13 '18 at 20:45
thesagniksahathesagniksaha
164115
164115
add a comment |
add a comment |
$begingroup$
Hint:
WLOG $b=1/a>0$
$$xy-1implies xdfrac{dy}{dx}+y=0impliesdfrac{dy}{dx}_{text{ at }(a,b)}=-dfrac{1/a}a=-dfrac1{a^2}$$
The equation of the tangent at $P,$ $$dfrac{y-1/a}{x-a}=-dfrac1{a^2}iff x+a^2y=2a$$
As $x$ axis, $y=0,$ the intersection will be $A(2a,0)$
$$|AP|=?, |OP|=?$$
$endgroup$
add a comment |
$begingroup$
Hint:
WLOG $b=1/a>0$
$$xy-1implies xdfrac{dy}{dx}+y=0impliesdfrac{dy}{dx}_{text{ at }(a,b)}=-dfrac{1/a}a=-dfrac1{a^2}$$
The equation of the tangent at $P,$ $$dfrac{y-1/a}{x-a}=-dfrac1{a^2}iff x+a^2y=2a$$
As $x$ axis, $y=0,$ the intersection will be $A(2a,0)$
$$|AP|=?, |OP|=?$$
$endgroup$
add a comment |
$begingroup$
Hint:
WLOG $b=1/a>0$
$$xy-1implies xdfrac{dy}{dx}+y=0impliesdfrac{dy}{dx}_{text{ at }(a,b)}=-dfrac{1/a}a=-dfrac1{a^2}$$
The equation of the tangent at $P,$ $$dfrac{y-1/a}{x-a}=-dfrac1{a^2}iff x+a^2y=2a$$
As $x$ axis, $y=0,$ the intersection will be $A(2a,0)$
$$|AP|=?, |OP|=?$$
$endgroup$
Hint:
WLOG $b=1/a>0$
$$xy-1implies xdfrac{dy}{dx}+y=0impliesdfrac{dy}{dx}_{text{ at }(a,b)}=-dfrac{1/a}a=-dfrac1{a^2}$$
The equation of the tangent at $P,$ $$dfrac{y-1/a}{x-a}=-dfrac1{a^2}iff x+a^2y=2a$$
As $x$ axis, $y=0,$ the intersection will be $A(2a,0)$
$$|AP|=?, |OP|=?$$
answered Dec 13 '18 at 14:22
lab bhattacharjeelab bhattacharjee
225k15157275
225k15157275
add a comment |
add a comment |
$begingroup$
The tangent line to $y=frac 1x$ at $P(x_0,y_0)$ is:
$$y=y_0+y'(x_0)(x-x_0)=frac 1{x_0}-frac 1{x_0^2}(x-x_0).$$
The point $A(x_1,0)$ has coordinate $x_1$:
$$0=frac 1{x_0}-frac 1{x_0^2}(x_1-x_0) Rightarrow x_1=2x_0,$$
which shows the triangle $PAO$ is isosceles, because the altitude $PB$ is the median too.
Now the area of $Delta PAO$ is:
$$S=frac 12 cdot AOcdot PB=frac12 cdot 2x_0 cdot frac1{x_0}=1.$$
$endgroup$
add a comment |
$begingroup$
The tangent line to $y=frac 1x$ at $P(x_0,y_0)$ is:
$$y=y_0+y'(x_0)(x-x_0)=frac 1{x_0}-frac 1{x_0^2}(x-x_0).$$
The point $A(x_1,0)$ has coordinate $x_1$:
$$0=frac 1{x_0}-frac 1{x_0^2}(x_1-x_0) Rightarrow x_1=2x_0,$$
which shows the triangle $PAO$ is isosceles, because the altitude $PB$ is the median too.
Now the area of $Delta PAO$ is:
$$S=frac 12 cdot AOcdot PB=frac12 cdot 2x_0 cdot frac1{x_0}=1.$$
$endgroup$
add a comment |
$begingroup$
The tangent line to $y=frac 1x$ at $P(x_0,y_0)$ is:
$$y=y_0+y'(x_0)(x-x_0)=frac 1{x_0}-frac 1{x_0^2}(x-x_0).$$
The point $A(x_1,0)$ has coordinate $x_1$:
$$0=frac 1{x_0}-frac 1{x_0^2}(x_1-x_0) Rightarrow x_1=2x_0,$$
which shows the triangle $PAO$ is isosceles, because the altitude $PB$ is the median too.
Now the area of $Delta PAO$ is:
$$S=frac 12 cdot AOcdot PB=frac12 cdot 2x_0 cdot frac1{x_0}=1.$$
$endgroup$
The tangent line to $y=frac 1x$ at $P(x_0,y_0)$ is:
$$y=y_0+y'(x_0)(x-x_0)=frac 1{x_0}-frac 1{x_0^2}(x-x_0).$$
The point $A(x_1,0)$ has coordinate $x_1$:
$$0=frac 1{x_0}-frac 1{x_0^2}(x_1-x_0) Rightarrow x_1=2x_0,$$
which shows the triangle $PAO$ is isosceles, because the altitude $PB$ is the median too.
Now the area of $Delta PAO$ is:
$$S=frac 12 cdot AOcdot PB=frac12 cdot 2x_0 cdot frac1{x_0}=1.$$
answered Dec 13 '18 at 16:24
farruhotafarruhota
20.2k2738
20.2k2738
add a comment |
add a comment |
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1
$begingroup$
Have you tried to find the tangent line in terms of $P$ yet?
$endgroup$
– SmileyCraft
Dec 13 '18 at 14:18
$begingroup$
Very good. So the slope of $PA$ is $-1/a^2$. Now if you also calculate the slope of $OP$ you should notice something which makes the triangle very symmetric.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:04
$begingroup$
So essentially, the slope of $OP$ is just the inverse of $PA$? @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:10
$begingroup$
Right, the additive inverse that is. Because $O$ and $A$ lie on the $x$-axis, it follows that $|PA|$=$|OP|$.
$endgroup$
– SmileyCraft
Dec 13 '18 at 15:12
$begingroup$
I see now. Thank you so much for your assistance! @SmileyCraft
$endgroup$
– Valèt Quasar
Dec 13 '18 at 15:13