If $\cos 43^\circ + \sin 43^\circ = k^3$, then $\cos 2^\circ = \ldots$

If the equation $\sin 3\theta - \cos^2\theta = \dfrac{1}{4}$ and $\theta \in [0, \pi]$, then the number of solutions is...

If $A(2, -3)$ and $C(-6, 7)$ are opposite vertices of a rhombus ABCD, then the equation of diagonal BD is

The measure of the acute angle between the pair of lines $2x^2 + xy - y^2 - x + 2y - 1 = 0$ is: