Question

Prove that:- sin 10° *cos 75°*sec 80° *cosec 15 = 1

Answer 1

Note: You will need to write the degree symbol for the arguments of these trigonometric functions.

As sin(x)=cos(90-x), this means sin10 = cos80 and cos75=15.

So,

LHS = (cos80)(sec80)(sin15)(cosec15)

LHS = (cos 80)(1/cos 80)(sin 15)(1/sin 15)

LHS = 1

Therefore, the identity is true.