Mathematics

Problem

Let

R

be the region bounded by

y=x^{2}

and

y=2x

0\le x\le 2

. When

R

is revolved about the x-axis, which pair of expressions gives the outer radius

R(x)

and the inner radius

r(x)

, respectively, for a typical cross section perpendicular to the x-axis? a)

R(x)=x^{2},\; r(x)=2x

R(x)=2x,\; r(x)=0

R(x)=2x,\; r(x)=x^{2}

R(x)=2x-x^{2},\; r(x)=0