Surface area of a cone is πr² + πrl: the base plus the slanted wrapper. l is slant height, not perpendicular height. Surface area as a set is in surface area.
Slant versus height
Volume uses perpendicular height, in volume of a cone. If the figure labels both, the lateral piece wants the slant. A sphere wrapping is 4πr², in surface area of a sphere.
The short list is in ACT Math formulas.
The bottom line
πr² + πrl. l is the slant, not the drop.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.