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
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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.
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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
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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
