Question #12d17

1 Answer
Jul 5, 2016

26) and 27)

Explanation:

26) We know that
cos(x-y)=Cos(x) Cos(y) + Sin(x) Sin(y)
and
cos^2x+sin^2x=1
then substituting
cos(x-y) = (sqrt[1 - (3/5)^2]) (5/13) + (3/5) sqrt[1 - (5/13)^2]

27) cos(2x) = sin x = cos(pi/2-x)
so
2x=pi/2-x+2k pi
solving for x
x = pi/6+2/3k pi for k = 0,pm1,pm2,...