Question

the total surface area of a right circular cone of slant hight 13 cm is 90πcm2. calculate it's radius​

Answer 1

Answer:

Radius = 5 cm

Volume = $314 cm^3$

Step-by-step explanation:

Total surface area of right circular cone = r(l+r)

90 = r(13+r)

90/ = r(13+r)

90 = $13r+r^2$

$r^2 + 13r - 90 = 0$

$r^2 + 18r - 5r + 90$ (By splitting the middle term)

r(r + 18) - 5(r+18) (By taking common)

(r-5)(r+18)

r = 5

r = -18 ( radius cannot be negative)

So, r = 5cm

l² = √h² + r²

13² = √h² + 5²

169 = √h² + 25

h = √169-25

h = √144

h = √12 cm

Volume of cone = 1/3h

= 1/3 * 3.14 * 5 * 5 * 12  

= $314 cm^3$

Answer 2

Answer:

radius is 5cm as we solving the question where l=13cm and total surface area is90 π