Maths completing square pt3 help plz

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Voss.gloss20
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#1
Report Thread starter 1 year ago
#1
Hey,

The question is y=4-7x-2x^2
I got up to -2(x-7/4)^2-49/8+4=0
After simplifying this, I don't get the answer given in the maths textbook.

I got -2(x-7/4)^2-17/8=0 then *-2
-2(x-7/4)^2+17/4=0

Which I said the turning point would be (7/4, 17/4). This is incorrect.

The actual turning point given in the textbook is (-7/4, 81/8)

What am I missing?
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Student 999
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You didn’t take into account when you divided -7x by -2.
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Voss.gloss20
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#3
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(Original post by Student 999)
You didn’t take into account when you divided -7x by -2.
Didn't I? I did it again and now got (-7/4, -17/8)
Still not got the full turning point
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mqb2766
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#4
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+49/8, not minus
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vc94
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y=4-7x-2x^2 = -2(x^2 + 7/2x) + 4 = -2[ (x + 7/4) - 49/16 ] + 4 ...
Try now...
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Voss.gloss20
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(Original post by vc94)
y=4-7x-2x^2 = -2(x^2 + 7/2x) + 4 = -2[ (x + 7/4) - 49/16 ] + 4 ...
Try now...
Thank you! Got the answer now
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Voss.gloss20
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(Original post by mqb2766)
+49/8, not minus
Thanks
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