Using The Argument Principle to Find How Many Zeros of a Function Are in a Region
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I'm a bit confused on the intuition on counting the number of zeros for a function in a given region using the Argument Principle. For example: Find the number of zeros of $f(z) = z^3 - 2z^2 + 4$ in the first quadrant. Since the function is analytic, there doesn't exist any poles, so we can say $frac{1}{2pi i}int_{gamma} frac{9z^8 + 10z}{z^9 + 5z^2 + 3} dz = N$ Where $gamma$ is the closed region encompassing the first quadrant, and $N$ is the number of zeros for $f(z)$ However, upon looking at the answers in my textbook I notice this integral is not explicitly used. In fact, the original function is parameterized for each part of the region and some information is derived from there. For example: On the Real line, we can substitute $z$ for $x$ , and we see $f(x) geq 2$ Bu...