Find the area $ A $ of a cone if radius $r = 9$ and slant height $l = 10$.

$A = 171\pi$

STEP 1: find base area $ AB $

To find base area $ AB $ use formula:

$$ AB = r^2 \cdot \pi $$

After substituting $ r = 9 $ we have:

$$ AB = 9^2 \cdot \pi $$ $$ AB = 81 \cdot \pi $$

STEP 2: find Curved Surface Area $ CSA $

To find Curved Surface Area $ CSA $ use formula:

$$ CSA = r \cdot l \cdot \pi$$

After substituting $ r = 9 $ and $ l = 10 $ we have:

$$ CSA = 9 \cdot 10 \cdot \pi$$$$ CSA = 9 \cdot 10 \cdot \pi $$$$ CSA = 90\pi $$

STEP 3: find area $ A $

To find area $ A $ use formula:

$$ A = AB + CSA $$

After substituting $ AB = 81\pi $ and $ CSA = 90\pi $ we have:

$$ A = 81\pi + 90\pi $$ $$ A = 81\pi + 90\pi $$ $$ A = 171\pi $$

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