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An equation i can't quite understand
By Jack Sutcliffe (P2879) on Thursday, September 7, 2000 - 08:52 pm:

Does anybody know HOW to do this equation as it would really help me a lot:

Solve the equation x2=5x+7 giving your answers correct to 3 sig. fig.

Thankyou for your help, this is probably easy for you but I just can't quite do it.

Cheers,
Jack.

P.S. I am 15 years old.
By Marion Palles-Clark (Mhp21) on Thursday, September 7, 2000 - 10:47 pm:

Hi Jack!

Do you remember being told the way to solve quadratic equations that you can't factorise?

Well, there is an equation as follows:

If

ax2 + bx + c = 0
then
x =
-b ±
Ö
b2-4ac
2a


So if you re-write your original equation in the form ax2 + bx + c = 0 (so you'll have x2 - 5x - 7 = 0) you should be able to work it out.

Don't forget you'll end up with 2 solutions!

Marion