Question

If sin A – cos A = 0, then the value of sin4 A + cos4 A is
(a) 2
(b) 1
(c) 34
(d) 12​

Answer 1

Answer:

Neither options, answer is -1

Step-by-step explanation:

sinA - cosA = 0

or, sinA = cosA

or, sinA = sin(90-A)     [cosA = sin(90-A)]

or, A = 90 - A

or, 2A = 90

or, A = 45

Again,

sin4A + cos4A = sin(4 X 45) + cos(4 X 45)

                         = sin180 + cos180

                          = 0 - 1

                          = -1