Question 24602
(1) {{{A = pi * r^2}}} is the formula for the area of a circle
your teacher gave you:
(2) {{{A = pi * (16*x^2 + 24*x + 9)}}}
so the terms in the parenthesis must represent {{{r^2}}}
if I find the square root of {{{r^2}}} I'll have r
{{{(16*x^2 + 24*x + 9) = (4*x + 3)^2}}}
{{{sqrt((4*x + 3)^2) = 4*x +3}}}
the square root can be + or - , but it makes sense to take the positive square root
so 4x + 3 is the radius