- #1

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- 0

## Homework Statement

How to integrate the double integral cos(x+y) dy dx from 0 to pi and from 0 to pi again.

## Homework Equations

The answer is -4.

## The Attempt at a Solution

Here's the work:

u=x+y

du=dy

cos(u)du=sin(x+y)

integral of [sin(x+y)] evaluate from 0 to pi dx from 0 to pi

integral of (sin(x+pi)-sin(x))dx from 0 to pi

And what's next?