Among the following, a correct statement is

The area of an isosceles triangle with base ‘b’ and equal side ‘a’ is $\frac{b}{4}\sqrt{4a^2-b^2}$.

If ‘d’ is the diameter of a circle, then area of a circle is $\frac{1}{4}\pi d^2$ sq. units.

The height of an equilateral triangle is $\frac{\sqrt{3}}{2}$ a where ‘a’ is the length of its side.

The perimeter of a right angled triangle whose lengths of the perpendicular sides are ‘x’ and ‘y’ is $x+y+\sqrt{x^2+y^2}$