Question

the total surface area of a right circular cone of slant height 13 cm is 90 pie CM square calculate
number 1) its radius in centimetre
number 2) its volume in centimetre cube [take pie = 3.14]

Answer 1

you can find volume =
$\frac{ 1}{3} \pi \:r ^{2}$

Answer 2

Hi, try using quadratic equations.

ur going to end up with-

90=r(13+r) (after canceling pi)

90+13r + r^2

0=-90+13r+r^2

0=-90+18r-5r+r^2

0=18(-5+r)+r(-5+r)

0=(18+r)(-5+r)

so, r=5cm

now, slant height= root of h^2+r^2

=12cm

olume=1/3.pi.r^2.h

=314.28cm^3

i hope u got ur ans.