Question

Which statement is false?

A. csc 20' = sec 70'
B. cos 87' = sin 3'
C. csc 40' = sin 50'
D. tan 15' = cot 75'

Answer 1

Answer: Option C. csc 40' = sin 50'
Because csc and sin are not cofunctions

Answer 2

Trigonometric functions which are related by having the same value at complementary angles are called cofunctions. Cofunctions of complementary angles are equal.

A. csc 20' = csc(90-70)=sec 70

B. cos 87' =  cos (90-3)=sin 3'

C. csc 40' =  csc(90-50) =sec50'  

D. tan 15' = tan(90-75)= cot 75'

Among all the option  c is not correct.

Option C is false.