The correct option is (A) \[{{r}^{2}}\] sq. units
Explanation:
The largest triangle which can be inscribed in a semi-circle of radius r units is
Base of triangle should be equal to the diameter of the semi-circle
The two other sides of triangle are taken by considering the point C on the circumference of the semi-circle and joining it by the end points of diameter A and B.
Therefore , \[\angle C={{90}^{\circ }}\] (by the properties of circle)
So, Triangle ABC is right angled triangle where base as diameter AB of the circle and height be CD.
Let Height of the triangle = r
Therefore, Area of largest \[\vartriangle ABC=(1/2)\times Base\times Height=(1/2)\times AB\times CD\]
We got \[(1/2)\times 2r\times r\]
= \[{{r}^{2}}\] sq. units
Hence Option A is correct.