Question

1+cos(8x)= ?

A 2cos^2(4x)
B 4cos(2x)
C 4sin(2x)
D 2sin^2(4x)

Answer 1

\(\bf 1+cos(8x)\implies 1+cos(2\cdot {\color{brown}{ 4x}})\implies \cancel{ 1 }+[2cos^2({\color{brown}{ 4x}})\cancel{ -1 }]\)

Answer 2

http://www.sosmath.com/trig/Trig5/trig5/img7.gif <--- double-angle identities

Answer 3

Thank you so much

Answer 4

yw