F(x)= radical sign (1+2)[ 1/ radical sign (1 2+2 2)sinx-2/ radical sign (1 2+2) cosx]

= radical sign 5sin(x+φ)

Because the three sides of a right triangle are 1, 2 and root number 5, sinφ=2/ root number 5, cosφ= 1/ root number 5, then tanφ=2.