SOLUTION: hi, my quadratic equation is (x+5)(x+8) =126.75 ive got these steps with help from a friend but as i need to show my working this wont be enough, i struggle with quadratics, what

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: hi, my quadratic equation is (x+5)(x+8) =126.75 ive got these steps with help from a friend but as i need to show my working this wont be enough, i struggle with quadratics, what       Log On


   

Question 620620: hi, my quadratic equation is (x+5)(x+8) =126.75
ive got these steps with help from a friend but as i need to show my working this wont be enough, i struggle with quadratics, what stages am i missing here?
X^2 + 13X – 86.75 =0
X=4.85782
X=4.85
thanks
Sam
Answer by MathTherapy(10858) About Me  (Show Source):
You can put this solution on YOUR website!

hi, my quadratic equation is (x+5)(x+8) =126.75
ive got these steps with help from a friend but as i need to show my working this wont be enough, i struggle with quadratics, what stages am i missing here?
X^2 + 13X – 86.75 =0
X=4.85782
X=4.85
thanks
Sam

You seem to have forgotten about the negative value of x. That's all!!

x%5E2+%2B+13x+-+86.75+=+0, with a = 1; b = 13; and c = - 86.75

Using the quadratic equationx+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+, we get:

x+=+%28-+13+%2B-+sqrt%28+13%5E2-4%2A1%2A-86.75+%29%29%2F%282%2A1%29+ ----- x+=+%28-+13+%2B-+sqrt%28+169+%2B+347%29%29%2F2+ ------ x+=+%28-+13+%2B-+sqrt%28516%29%29%2F2+

x+=+%28-+13+%2B-+%2822.71563338%29%29%2F2+

x+=+%28-+13+%2B+22.71563338%29%2F2+, or x+=+%28-+13+-+22.71563338%29%2F2+

x+=+%289.71563338%29%2F2+, or x+=+%28-+35.71563338%29%2F2+

highlight_green%28x+=+4.85781669%29, or highlight_green%28x+=+-+17.85781669%29

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