Question 761723


7sin^2x + cos^2x = 4

Split the 7 on the left hand side as 6 and 1

6sin^2x + sin^2x + cos^2x = 4  

Since sin^2x + cos^2x = 1

6sin^2x + 1 = 4

6sin^2x = 3

sin^2x = 1/2

sin x = 1/sqrt(2) or -1/sqrt(2)

Therefore

cos x = 1/sqrt(2) or -1/sqrt(2)  (cos x = sqrt (1 - sin^2x)

:)