calculate angle of line with negative slope












0












$begingroup$


I want to use the formula
$$
tan(alpha)=m
$$
for negative slopes but always get negative degrees. For instance, say the slope of a line $g$ is $-1$. Using the formula above (arctan$(-1)=alpha$), I get $-45$ degrees instead of $135$ degrees.
Why exactly does this formula not returning correct angles for negative slopes?






angle slope







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$endgroup$












  • $begingroup$
    It all depends on how you define $arctan$. It is usually defined as the inverse function of the restriction of $tan$ on $left( -frac{pi}{2}, frac{pi}{2}right)$.
    $endgroup$
    – Bill O'Haran
    Dec 18 '18 at 10:12
















0












$begingroup$


I want to use the formula
$$
tan(alpha)=m
$$
for negative slopes but always get negative degrees. For instance, say the slope of a line $g$ is $-1$. Using the formula above (arctan$(-1)=alpha$), I get $-45$ degrees instead of $135$ degrees.
Why exactly does this formula not returning correct angles for negative slopes?






angle slope







share|cite|improve this question









$endgroup$












  • $begingroup$
    It all depends on how you define $arctan$. It is usually defined as the inverse function of the restriction of $tan$ on $left( -frac{pi}{2}, frac{pi}{2}right)$.
    $endgroup$
    – Bill O'Haran
    Dec 18 '18 at 10:12














0












0








0





$begingroup$


I want to use the formula
$$
tan(alpha)=m
$$
for negative slopes but always get negative degrees. For instance, say the slope of a line $g$ is $-1$. Using the formula above (arctan$(-1)=alpha$), I get $-45$ degrees instead of $135$ degrees.
Why exactly does this formula not returning correct angles for negative slopes?






angle slope







share|cite|improve this question









$endgroup$




I want to use the formula
$$
tan(alpha)=m
$$
for negative slopes but always get negative degrees. For instance, say the slope of a line $g$ is $-1$. Using the formula above (arctan$(-1)=alpha$), I get $-45$ degrees instead of $135$ degrees.
Why exactly does this formula not returning correct angles for negative slopes?






angle slope




angle slope






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Dec 18 '18 at 10:07









lagunalaguna

767




767












  • $begingroup$
    It all depends on how you define $arctan$. It is usually defined as the inverse function of the restriction of $tan$ on $left( -frac{pi}{2}, frac{pi}{2}right)$.
    $endgroup$
    – Bill O'Haran
    Dec 18 '18 at 10:12


















  • $begingroup$
    It all depends on how you define $arctan$. It is usually defined as the inverse function of the restriction of $tan$ on $left( -frac{pi}{2}, frac{pi}{2}right)$.
    $endgroup$
    – Bill O'Haran
    Dec 18 '18 at 10:12
















$begingroup$
It all depends on how you define $arctan$. It is usually defined as the inverse function of the restriction of $tan$ on $left( -frac{pi}{2}, frac{pi}{2}right)$.
$endgroup$
– Bill O'Haran
Dec 18 '18 at 10:12




$begingroup$
It all depends on how you define $arctan$. It is usually defined as the inverse function of the restriction of $tan$ on $left( -frac{pi}{2}, frac{pi}{2}right)$.
$endgroup$
– Bill O'Haran
Dec 18 '18 at 10:12










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Use this formula: $alpha=begin{cases}tan^{-1}m,&mge0\pi+tan^{-1}m,&m<0end{cases}$






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    0












    $begingroup$

    Use this formula: $alpha=begin{cases}tan^{-1}m,&mge0\pi+tan^{-1}m,&m<0end{cases}$






    share|cite|improve this answer









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      0












      $begingroup$

      Use this formula: $alpha=begin{cases}tan^{-1}m,&mge0\pi+tan^{-1}m,&m<0end{cases}$






      share|cite|improve this answer









      $endgroup$
















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        $begingroup$

        Use this formula: $alpha=begin{cases}tan^{-1}m,&mge0\pi+tan^{-1}m,&m<0end{cases}$






        share|cite|improve this answer









        $endgroup$



        Use this formula: $alpha=begin{cases}tan^{-1}m,&mge0\pi+tan^{-1}m,&m<0end{cases}$







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered Dec 18 '18 at 10:11









        Shubham JohriShubham Johri

        5,192717




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