9514 1404 393
Answer:
15 cm
Step-by-step explanation:
The formula for the surface area of the cone is ...
A = πr² +πrL = πr(r +L)
The radius of this cone is half its diameter so is (12 cm)/2 = 6 cm. Then the slant height L can be found from ...
126π cm² = π(6 cm)(6 cm +L)
21 cm = 6 cm +L . . . . . . . . . . . . . . divide by 6π cm
15 cm = L . . . . . . . . . . . . . . . . subtract 6 cm
The slant height is 15 centimeters.
