Answer
$A=\frac{1}{2}absin\theta$
Work Step by Step
Area of a triangle is given by
$A=\frac{1}{2}\times Base\times Height$
Here, base =b and height =h
In order to find height, we will consider
$sin\theta=\frac{opp}{hyp}=\frac{h}{b}$
$h=bsin\theta$
Thus, $A=\frac{1}{2}\times a\times bsin\theta$
Hence, $A=\frac{1}{2}absin\theta$