Question

Помогите решить cos (2arctg1 - arccos 5/13)

Answer 1

2arctg1=2*$45^{0}$=90, cos90=0, sin90=1
cos(90-arccos5/13)=cos90*cosarccos5/13+sin90*sinarccos5/13=sinarccos5/13=√1-5^2/13^2=√1-25/169=√144/169=12/13