justinee
Can someone check this for me? (completing the square)



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justinee
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y = 2x^2  20x  48

justinee
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then i rewrote that into:
y = 2(x^2  20x ____) 48
20/2 = 10 then square it and I got 100
y = 2(x^2  20x +100) 48

justinee
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then I added 100 to both sides and I got:
y + 100= 2(x  10)^2 48
100 100

y = 2(x  10)^2  148

halorazer
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You subtracted 100 though ^

Decart
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you add 48 to the other side and then also the 100 and the quadratic = 148

Decart
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then you can factor the left side

justinee
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can you show me that in steps? like from the beginning

Decart
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you did it rite just set the equation = 0
then subtract 49 from both sides so
2x^220x=48

Decart
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then complete the square and add the 100 to both sides

justinee
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so it'd be 0 = 2(x^2  20x + 100) 48 ?

justinee
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why do I need to factor that

justinee
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Ok I got it thanks! and one more question

justinee
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How would I solve:
x^2  38x + c
also by completing the square

Decart
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c is a constant most likely just move it to the other side and complete the square

justinee
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what is that going to give me?

Decart
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x^238x=c

justinee
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and what would be the next step

justinee
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0 = (x2  38x ___) +c ?

Decart
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square the 38 and do the same to both sides

Decart
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(x^238x+__)=__c

justinee
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38/2 = 19^2 = 361

Decart
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yup

Decart
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so that is on both sides

Decart
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(x^238x+361)=361c

justinee
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okay so far i have:
(x^2  38x + 361) = 361 c

Decart
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right now you should be able to factor the quadratic
which is the point of completing the square

justinee
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so like:
____ x___ = 361
____+___= 38

Decart
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right
it will be the same number it is squared

justinee
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19

Decart
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yup

justinee
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(x19)^2 = 361  c?

Decart
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and the first equation was x^210+25=49

Decart
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right

justinee
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what do I do now?

Decart
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with the second you can't do anything it is most likely to show how you did the work

Decart
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x5=7

justinee
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so just that ^

justinee
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how would i write tht in intercept form

Decart
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do you mean y=mx+b

justinee
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no I also have to rewrite tht in intercept

Decart
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the x intercept is +or(7/5,0)

Decart
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that is the y is 0