cos 13 pi = ?

Answer 1

cos 13π
= cos( 4(2π) + π) , 13π is 4 rotations + π
= cosπ
= -1

Answer 2

cos13pi
= cos 13pi*180/pi
=cos2340degree
= cos(7*360-180)
= cos(180degree)
= -1
hope u understood:)