# How to go from the first expression to the second

### How to go from the first expression to the second

$$\int\limits_{0}^{\infty} e^{i\vec{k}(\vec{y}-\vec{x})}\vec{k}^{-2}d^3k$$ = $$\int\limits_{0}^{2\pi} d\varphi\int\limits_{-1}^{1} d cos\lambda \int\limits_{0}^{\infty} d|\vec{k}|e^{i cos\lambda|\vec{k}||\vec{x}-\vec{y}|}$$
Guest

### Re: How to go from the first expression to the second

I have no idea what the first expression is saying! You appear to have a vector, $$\vec{k}$$ to a negative power. How are you defining a vector to a power?

HallsofIvy

Posts: 341
Joined: Sat Mar 02, 2019 9:45 am
Reputation: 119

### Re: How to go from the first expression to the second

$$\vec{k}^{-2}=1/\vec{k}^2$$. And $$\vec{k}^2$$ is just the square of the norm of the vector. So it is just a number.
Guest