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## #1 2006-04-17 08:50:12

RickyOswaldIOW
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Happy Easter everyone!

I've just been revising some of my earlier a-level work and I'm a little confused with this:

"Let f(x) = x^2 + 6x + 7.

(a)  Put f(x) into completed square form.

(b)  Solve the equation f(x) = 4."

I do know how to do all of this but I can't for the life of me see where they are getting f(x) = 4 from?!

Aloha Nui means Goodbye.

## #2 2006-04-17 08:55:09

RickyOswaldIOW
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Are they just saying that for the sake of the example that (x + 3)^2 - 2 = 4?  That's mighty confusing since the next 50 pages that often use factorising and completing the square assume that f(x) = 0.

Aloha Nui means Goodbye.

## #3 2006-04-17 14:41:32

George,Y
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Typically, you shift the original function into a form
f(x) = (x+a)²+b

It does no matter that the function equal to any given value, because the equation formed can be easily solved.

f(x)=c
(x+a)²=c-b

or

hence

Actually, given a equation of standard form, the explicit solution fomula is derived by this procedure
ax²+bx+c=0
a(x+b/2a)²=b²/4-c
......

X'(y-Xβ)=0

## #4 2006-04-22 10:09:46

dimples
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how can i write a two paragraph essay on "Solving Quadratic Equations by the Quadratic Formula"

MathsIsFun

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