Use the appropriate half angle double angle or addition form

Use the appropriate half angle, double angle, or addition formula to find the EXACT value of the following expressions. Simplify your answer as much as possible. (Don\'t use your calculator. You must SHOW all the correct algebraic steps for credit. No decimals!) a) cos(9 pi/8) b) sin (49 degree)cos (11 degree)+ cos (49 degree)sin(11 degree)

Solution

a) cos(9*pie/8)

= cos( pie + pie/8)

= -cos(pie/8) =-0.9238795 = -0.923

b)sin(49)cos(1)+cos(49)sin(1) = sin(49+1) = sin(50)

The given one is in the form of sin(A+B) = sin(A) cos(B) +cos(A)sin(B)