Subtract the sine term and take the square root.

Answer:
Step-by-step explanation:
x² + 4x - 1 - x =x² + 4x -x - 1 { bring the like terms together and add}
= x² + 3x - 1


we switched side of -6 and added it to 2
2x + 10 = 64 now we squared both sides to get rid of square root
2x = 54 we switched side of +10 and subtracted it from 64
x = 27 we divided both sides with 2
answer is x = 27