The correct option is C cos(5π2−θ)
Given an acute angle θ and we have to find which of the following trigonometric functions have a positive value.
a. sin(3π2−θ)
3π2−θ corresponds to angle in the third quadrant where both sin and cos are negative.
⇒sin(3π2−θ)=−cosθ
Hence, it's value will be negative.
b. cos(5π2−θ)
5π2−θ corresponds to an angle in the first quadrant where all trigonomettric functions are positive.
⇒cos(5π2−θ)=+sinθ
Hence, it's value will be positive.
c. sec(7π2+θ)
7π2+θ corresponds to angle in the fourth qudrant where sec of an angle is positive..
⇒sec(7π2+θ)=cosec θ
Hence, it's value will be positive.
d. cosec (5π2+θ)
5π2+θ corresponds to angle in the second qudrant where cosec of an angle is positive.
⇒cosec (7π2+θ)=secθ
Hence, it's value will be positive.