Find all solutions to the equation: cos x = sin x

Divide both sides by cos[x] 

You get 1 = Tan[x] 

Tan[x] = 1 where x = 45 degrees {+ integer multiples of 180 degrees due to periodicity of tan} 

x = 45 + 180*k OR Pi/4 + kPi, for k any integer

Cosx=sinx
sin(pi/2-x)=sinx
pi/2-x=x
pi/2=x+x
pi/2=2x
x=pi/4
45 degrees
hope it helps