Find the area $ A $ of a cone if diameter $d = 26$ and slant height $l = 11$.

$A = 312\pi$

STEP 1: find radius $ r $

To find radius $ r $ use formula:

$$ d = 2 \cdot r $$

After substituting $ d = 26 $ we have:

$$ 26 = 2 \cdot r $$ $$ r = \dfrac{ 26 }{ 2 } $$ $$ r = 13 $$

STEP 2: find base area $ AB $

To find base area $ AB $ use formula:

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

After substituting $ r = 13 $ we have:

$$ AB = 13^2 \cdot \pi $$ $$ AB = 169 \cdot \pi $$

STEP 3: find Curved Surface Area $ CSA $

To find Curved Surface Area $ CSA $ use formula:

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

After substituting $ r = 13 $ and $ l = 11 $ we have:

$$ CSA = 13 \cdot 11 \cdot \pi$$$$ CSA = 13 \cdot 11 \cdot \pi $$$$ CSA = 143\pi $$

STEP 4: find area $ A $

To find area $ A $ use formula:

$$ A = AB + CSA $$

After substituting $ AB = 169\pi $ and $ CSA = 143\pi $ we have:

$$ A = 169\pi + 143\pi $$ $$ A = 169\pi + 143\pi $$ $$ A = 312\pi $$

Cone Calculator