# Show me how this equation is valid

1. May 28, 2014

### oahz

Please, hurry. It's driving me nuts

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2. May 28, 2014

### economicsnerd

I suppose $f \geq 0$? If so, $y\geq x \implies yf(y) \geq xf(y)$.

3. May 28, 2014

### Nick O

Seconded. Note that y takes on every value >= x, so you have basically replaced the constant x with the increasing function y in the integral.