Question

plz answer this question.

Answer 1

1+3cos2x = 1+cos2x
1-1 = 3cos2x-cos2x
2cos2x = 0
cos2x = 0
cos x = 0
x =  0

Answer 2

The correct answer is:
-1<=cosx<=1
-3<=3cosx<=3. (Multiply 3)
-3+1<=1+3cosx<=3+1. (Add 1)
-2<=f(x)<=4
Thus the range is [-2,4]