Question

How would I do this?

Answer 1

a == 5 Cos[pi/2 - ArcTan[5/12]] = 25/13
b == 5 Sin[pi/2 - ArcTan[5/12]] = 60/13\[\sqrt{\left(\frac{25}{13}\right) ^2+\left(\frac{60}{13}\right)^2}=5 \]