The equation 6^x + 8^x = 10^x has

$$\cos (2x + 7) = a(2 - \sin x)$$ can have a real solution for

Let f(x) = sin x + cos ax be periodic function. Then,

If $${e^{\sin x}} - {e^{-\sin x}} - 4 = 0$$, then the number of real values of x is