x^2+3x-2=0 Solve for x completing the square  TOPIC_SOLVED

Quadratic equations and inequalities, variation equations, function notation, systems of equations, etc.

x^2+3x-2=0 Solve for x completing the square

Postby pistolpete on Wed May 20, 2009 1:09 am

x^2+3x-2=0

I have to solve for x by completing the square

I am a bit slow and get stuck at this part:
x^2+3x-2=0
x^2+3x=2
x^2+3x+2.25=4.25
(x+ )(x+ )=4.25

I can't factor the 2.25 to get 3. Or am i doing this wrong???
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Re: x^2+3x-2=0 Solve for x completing the square

Postby pistolpete on Wed May 20, 2009 3:14 am

nevermind i got it thanks..
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  TOPIC_SOLVED

Postby stapel_eliz on Wed May 20, 2009 11:36 am

pistolpete wrote:x^2+3x-2=0

I have to solve for x by completing the square

For other readers:

To complete the square to solve this quadratic, the steps are as follows:

. . . . .

. . . . .

Take half of +3, square it, and add to both sides:

. . . . .

Convert the left-hand side, using the +3/2, to perfect-square form:

. . . . .

. . . . .

. . . . .

...and so forth. :wink:
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Re: x^2+3x-2=0 Solve for x completing the square

Postby pistolpete on Wed May 20, 2009 12:03 pm

I did it by the use of decimals.

x^2+3x+2.25=4.25
(x+1.5) (x+1.5)=4.25
(x+1.5)^2=4.25

sqgrt both sides

x+1.5=sgrt(4.25)
-1.5 -1.5

x= -1.5 +-sgrt(4.25)

is this correct also?
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Postby stapel_eliz on Wed May 20, 2009 2:11 pm

If you are allowed to format the answers using decimals, then yes, your answer is "right". But most books and instructors don't like the decimal form, even though the value is exactly the same. :shock:

Check with your instructor to be sure. :wink:
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