The GATE Grind

GATE 2016 EC (EC3) – Question 12

Engineering Mathematics · Complex Analysis · 1 mark · Numerical answer

For $f(z)=\sin z/z^2$, the residue at the pole z=0 is ________.

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: 1.0 to 1.0

Explanation

Expand $\sin z=z-z^3/3!+z^5/5!-\cdots$. Dividing by $z^2$ gives $f(z)=1/z-z/6+z^3/120-\cdots$.

The residue is the coefficient of $z^{-1}$ in the Laurent series, hence **1**. The apparent squared denominator leaves only a simple pole because sin z has a zero at the origin.

More Complex Analysis questions

All Complex Analysis questions →