Question

please answer my question, If you answer is correct I'll make you a brainy.

Answer 1

$tan \alpha = \frac{sina - cosa}{sina + cosa} \\ \: \: \: \: \: \: \: \: \: \: = \: \frac{tana - 1}{1 + tana} \\ \: \: \: \: \: \: \: \: \: \: = \tan(a - \ \ \frac{\pi}{4} ) \\ \: \: \: \: \: \: \: \: \: \: \ \: so \: \alpha = a - \frac{\pi}{4} \\ \: \: \: \: \: \: \: \: \: \: sin \alpha = \sin(a - \frac{\pi}{4} ) \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = \frac{sina - cosa}{ \sqrt{2} }$