alainabbyboo22 3 years ago Find the surface area of the figure below. A. 203.1 ft2 B. 301.59 ft2 C. 318.74 ft2 D. 395.84 ft2 i am so confused on this .. i am trying to use the c^2=b^2 and a^2 different ways but its just not working out . what am i doing wrong ?

1. alainabbyboo22

2. alainabbyboo22

@gaara438125

3. gaara438125

we need to find the height first, which i believe we already found was 16.16 correct?

4. alainabbyboo22

this is a completely different question than before . lol . i'm so unsure with this one .

5. gaara438125

ok i see what's different :P we need to find a side (the height) we know the hypotenuse (the slant) and one side so b^2 = c^2 - a^2 c = 15 a = 6

6. alainabbyboo22

my answer was 189 . what do i do from there ? because that answer isn't available in the answer choices .

7. alainabbyboo22

@gaara438125 @JakeV8 @Grim0519

8. JakeV8

You were close... just not done with the last step on finding that length: b^2 = c^2 - a^2 c = 15 a = 6 b^2 = 225 - 36 b^2 = 189 But you want "b", not "b squared"... you forgot to take the square root of 189.

9. mayankdevnani

do you know the surface area of cone=?

10. JakeV8

But then, yeah, you need surface area, not just the length of the outside edge. I don't have that formula handy...

11. mayankdevnani

you are right @JakeV8

12. alainabbyboo22

the square root of 189 is : 13.7477270849

13. JakeV8

I'm not sure you needed to find that after all... but good practice with the pythagorean theorem :) The formula for surface area of a cone needs the diagonal length, not the height. The formula I found online (yay Internet!) was: pi * r^2 + pi * r * s where "r" is the radius (shown as 6) and "s" is the diagonal length of the cone's edge, (shown as 15).

14. JakeV8
15. alainabbyboo22

woot woot ! got my answer (: 395.84 ft^2 (: (: (:

16. JakeV8

Good work... you just needed to use the formula.

17. alainabbyboo22

thank you so much for helping me out (:

18. JakeV8