Question

sin^4(x)+cos^4(x) = 5/8

Answer 1

how to solve this?

Answer 2

mathway.com

Answer 3

Let cos^2(x)=a
Sin^2(x)=1-cos^2(x)=1-a
Then we have (sin^2(x))^2+a^2=5/8
This is. (1-a)^2+a^2=5/8
I trust you can do the rest