If $\tan^{-1} \left(\frac{1}{2}\right)+\tan^{-1} \left(\frac{x}{3}\right)=\frac{\pi}{4},$ where 0 < x < 6, then what is x equal to?

If 3 sin^-1x + cos^-1x = π, then what is x equal to?

If tan α + tan β = 1 - tan α.tan β, where tan α tan β ≠ 1, then which of the following is one of the values of (α + β) ?

If (1 + tan θ) (1 + tan 9θ) = 2, then what is the value of tan(10θ)?