Find all solutions to the equation in the interval [0, 21).
COS X = sin 2x

A. Pi/2, 3pi/2
B. Pi/6, pi/2, 5pi/6, 3pi/2
C. 0, pi
D. 0, pi/6, 5pi/6, pi

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.