# Completing the Square

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Thread starter 4 weeks ago
#1
GCSE Maths CGP The Student Book P137, Ex 1, Q3, H
Rewrite the quadratics below in the form (x +p)^2 =+ q

X^2 - 9x - 25

(x+p)^2 + q , p=b/2=(-9/2)
(x -9/2)(x - 9/2) = x^2 - 9x/2 - 9x/2 + 181/4
= x^2 - 9x + 181/4 (181/4 = 42.25)

so I need to get from +181/4 to (-25)
Therefore, 181/4 + (-25) = -281/4 = q
(x - 9/2)^2 - 281/4

However book answer is : (x - 9/2)^2 - 181/4
Is like they've ignored the -25
0
4 weeks ago
#2
(Original post by DJFearRoss)
GCSE Maths CGP The Student Book P137, Ex 1, Q3, H
Rewrite the quadratics below in the form (x +p)^2 =+ q

X^2 - 9x - 25

(x+p)^2 + q , p=b/2=(-9/2)
(x -9/2)(x - 9/2) = x^2 - 9x/2 - 9x/2 + 181/4
= x^2 - 9x + 181/4 (181/4 = 42.25)

so I need to get from +181/4 to (-25)
Therefore, 181/4 + (-25) = -281/4 = q
(x - 9/2)^2 - 281/4

However book answer is : (x - 9/2)^2 - 181/4
Is like they've ignored the -25
Expand it out and compare to the original ... but 9 x 9 is not 181 btw
0
4 weeks ago
#3
An example of another question would be: write x^2 +4x -6 in the form (x+p)^2 +q. To do this you would half the number with the x (4) and move the indice (^2)from the x to the outside of a bracket. After you do this you need to minus the square of the number you halved. This would look like (x+2)^2 -4 , and the -6 is still there so u put it back making it (x+2)^2-4 -6 which simplifies to (x+2)^2 -10 which would be your final answer.
In your question it is slightly more confusing as the number with the x is a 9 and half of that is 9/2 and thus you have fractions but either way you do the same as you do here.
Last edited by Okayn; 4 weeks ago
0
4 weeks ago
#4
(Original post by Okayn)
I see what you've tried to do
Please edit - it's against forum rules to post a solution
0
4 weeks ago
#5
(Original post by Muttley79)
Please edit - it's against forum rules to post a solution
My bad I didn't know I'll rewrite it.
1
Thread starter 4 weeks ago
#6
(Original post by Okayn)
My bad I didn't know I'll rewrite it.
I didn't know that either!
0
Thread starter 4 weeks ago
#7
(Original post by Okayn)
An example of another question would be: write x^2 +4x -6 in the form (x+p)^2 +q. To do this you would half the number with the x (4) and move the indice (^2)from the x to the outside of a bracket. After you do this you need to minus the square of the number you halved. This would look like (x+2)^2 -4 , and the -6 is still there so u put it back making it (x+2)^2-4 -6 which simplifies to (x+2)^2 -10 which would be your final answer.
In your question it is slightly more confusing as the number with the x is a 9 and half of that is 9/2 and thus you have fractions but either way you do the same as you do here.
Thanks, i'll try that.
0
Thread starter 4 weeks ago
#8
(Original post by Muttley79)
Expand it out and compare to the original ... but 9 x 9 is not 181 btw
Thanks. Not sure where I got 181.
So i changed it to 81 and now I get the same answer as the book, so job done.
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