cone has a circular base, a perpendicular height of 42cm and asemivertical angle of of 30. Calculate the slant height of the cone
"asemivertical" = a semi vertical ?????
so your cross-section is a right-angled triangle with height 42 and slant
height of s, and the angle at the top is 15°.
clearly:
cos 15° = 42/s
s = 42/cos 15° = .......