Question

Trigonometry: If f(x)= 2sinx + cosx using exact values find f (120 degrees). if possible show steps.

Answer 1

Answer: f(120°) = (√3) + 1/2

Step-by-step explanation:

i will solve it with notable relations, because using a calculator is cutting steps.

f(120°) = 2*sin(120°) + cos(120°)

           =2*sin(90° + 30°) + cos(90° + 30°)

here we can use the relations

cos(a + b) = cos(a)*cos(b) - sin(a)*sin(b)

sin(a + b) = cos(a)*sin(b) + cos(b)*sin(a)

then we have

f(120°) = 2*( cos(90°)*sin(30°) + cos(30°)*sin(90°)) +  cos(90°)*cos(30°) - sin(90°)*sin(30°)

and

cos(90°) = 0

sin(90°) = 1

cos(30°) = (√3)/2

sin(30°) = 1/2

We replace those values in the equation and get:

f(120°) = 2*( 0 +  (√3)/2) + 0 +  1/2 = (√3) + 1/2