Pls ! will mark !

these 4 questions answered and work shown

for reference): topics: trig functions exact values and reciprocal trig functions exact values

Answer:

25) If f(x) = sin ([1/3] x) , find f(π/2).

Substitute with x = π/2

f(π/2) = sin ([1/3] *[π/2]) = sin (π/6) = 1/2

26) If f(x) = cos (2x) , find f(3π/4).

Substitute with x = 3π/4

f(3π/4) = cos ( 2 * 3π/4) = cos ( 3π/2) = zero.

27) If f(x) = sin (2x) + cos (3x) , find f(π/4)

Substitute with x = π/4

f(π/4) = sin ( 2 * π/4) + cos ( 3 * π/4) =

        = sin ( π/2) + cos ( 3π/4)

        =  1  - 1/(√2)

        = 0.293

28) f(x) = tan (5x) - sin (2x) , find f(π/6).

Substitute with x = π/6

So, f(π/6) = tan (5 * π/6) - sin ( 2 * π/6)

               = tan (5π/6) - sin (π/3)

               = -1/(√3) - (√3)/2

                = -1.443