Does not understand trig identity cos 2x = 1 − 2 sin(x)^2

[Whodiduexpect]

> cos 2x = 1 − 2 sin(x)^2

  cos((2 × x) radians) = (1 − (2 × sin(x radians)²))

  cos(2x) + 2 × sin(x)² = 1

This should evaluate to true. This can cause libqalculate to fail to isolate x on seemingly simple equations.