# I Magnetic field due to a straight wire

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1. Oct 30, 2018

### Celso

Can someone help me to understand some of these steps?
Why can we write $\frac{1}{R} = \frac{sin(\phi)}{R}$ and $y = - cot(g\phi)$?

2. Oct 30, 2018

### Arman777

The derivations are written. Which part didnt you understand exactly ?