Which of the following errors is not detected by Trial

Simplify the following trigonometric expression: 

15 cos 25° cosec 65° − 5 cot 80° cot 10°

Given that tan(A+B) = √3 and tan(A-B) =1/√3, find the values of A and B.

If cos 2x = 1/2, then the value of x:

If cos2B = sin(1.5B + 27 ^o), then find the measure of 'B'. 

If Sin θ + Cos θ = √2 Cos(90 - θ ), then find the value of Cot θ ?

Find the value of the given expression.

3 × (sin 30° + cos 60°)

If sec(2A + B) = 2 and cos(A + B) = (1/√2) , find the value of {sec 2B + tan (A + B) } given that 0^o < A, B < 90^o

If  tan 12θ x tan 6θ = 1 then the value of tan 9θ is