Question

I want to know the answer of this question

Answer 1

$\bf \textit{circumference of a circle}\\\\ C=2\pi r\qquad \begin{cases} r=radius\\ -----\\ r=5x^2 \end{cases}\implies C=2\pi 5x^2\implies C=10\pi x^2 \\\\\\ \textit{area of a circle}\\\\ A=\pi r^2\qquad \begin{cases} r=radius\\ -----\\ r=5x^2 \end{cases}\implies A=\pi (5x^2)^2\implies A=\pi (5^2x^{2\cdot 2}) \\\\\\ A=\pi (25x^4)\implies A=25\pi x^4$