Answer
Express $\theta$ in terms of $\alpha$ and $\beta$.
$$\theta=\beta-\alpha$$
Work Step by Step
In triangle $ABC$, $\angle A=\alpha$ and $\angle B=180^\circ-\beta$ and $\angle C=\theta$.
Since the sum of 3 angles in a triangle reaches $180^\circ$, we can calculate $\angle C$, and thus express $\theta$, in terms of $\alpha$ and $\beta$.
$$\angle A+\angle B+\angle C=180^\circ$$
$$\alpha+180^\circ-\beta+\theta=180^\circ$$
$$\theta=180^\circ-\alpha-180^\circ+\beta$$
$$\theta=\beta-\alpha$$
$\theta$ has been expressed in terms of $\alpha$ and $\beta$.
