Question

I have an equation like this:

2pi(r)^2+14pi(r)-231=0

How can I find the value of r?

Answer 1

use pi =22/7 and then it will com in in simpler terms...

Answer 2

further solve the quadratic...

Answer 3

Could you please show me?

Answer 4

???

Answer 5

(44/7)(r^2)=A
(308/7)(r)=B
-231=C
for the quadratic formula, let x=r

Answer 6

Couldn't I just let x = pi x r ??

Answer 7

@ganeshie8 I tried to do that but it gave me a different answer

Answer 8

Ax^2+Bx+C=0 That't the standard form.
the x, in this case is r. The variable changed, but that shouldn't affect the value.

Answer 9

Are you typing it in on your calculator incorrectly?

Answer 10

http://www.wolframalpha.com/input/?i=solve+2pi*r%5E2%2B14pi*r-231%3D0

Answer 11

I'm doing it manually

Answer 12

wolfram has the correct quadratic formula format
look it up

Answer 13

So I can't let x = pi x r ??

Answer 14

No

Answer 15

\( \color{red}{2\pi} r^2+\color{red}{14\pi} r \color{red}{-231}=0\)

Answer 16

why do you want to let x = pi x r ?

Answer 17

So that it takes the quadratic form of ax^2 + bx + c

Answer 18

its already in the quadratic form :

\(\color{red}{2\pi} r^2+\color{red}{14\pi} r \color{red}{-231}=0 \)

\(a = \color{red}{2 \pi}\)
\(b = \color{red}{14 \pi}\)
\(c = \color{red}{-231}\)

Answer 19

And yes, \(\color{red}{\pi}\) is just a number

Answer 20

if u prefer, u may put \(x = r\)

Answer 21

Thank you for the explanation :)

Answer 22

np :)

Answer 23

I have one more question

Where did 44/7 r^2 come from?

Answer 24

I just multiplied it by 2.

Answer 25

Could you please show me?

Answer 26

2(22/7)
2*22=44
44/7

Answer 27

There ya go.

Answer 28

And the 22/7?

Answer 29

That's what pi represents as a fraction.

Answer 30

Thank you

Answer 31

No problem! Anytime! :)