Question

the radius of a cylindrical gift box is ​(2x+3​) inches. The height of the gift box is twice the radius. What is the surface area of the​ cylinder?

Answer 1

Since the surface area formula is 2πrh+2πr², we can plug 2x+3 in for r and 2*(2x+3)=4x+6 in for h to get 2π(2x+3)(2)(2x+3)+2π(2x+3)²=4π(2x+3)²+2π(2x+3)²=2π(2x+3)²(2+1)=6π(2x+3)²
=6π(4x²+12x+9)