If tan-1(1/2) + tan-1(x/3) = π/4, where 0 < x < 6, then what is x equal to?

The value of cos(sin-1(513)) is equal to:

The solution of the equation 3 tan-1(x) - 2 cot-1(x) = π2 in the first quadrant is ________.

If sin-1(1 - x) - 2sin-1(x) = π2, then find the value of x.