Question

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

Answer 1

\[4\frac{ 1+\cos 2x }{2 }+\frac{ 1-\cos 2x }{2 }=0\]
4+4cos 2x+1-cos 2x=0
3 cos 2x=-5
cos 2x=-5/3
impossible as \[\left| \cos 2x \right|\le 1\]