SOLUTION: My book says the answer is -5 and -3, where am I missing it? {{{x^2-8x-15=0}}} x={{{(-(-8)+- sqrt(-8^2-4*1*15))/(2*1)}}} x={{{8+- sqrt (64-60)/(2)}}} x={{{8+- sqrt (4)/(2)}}}

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Question 259973: My book says the answer is -5 and -3, where am I missing it?

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Answer by nerdybill(7384)   (Show Source): You can put this solution on YOUR website!
You are both wrong!
.
Your mistake:

x= <--Here -- should be -15
.
Unless your original equation has a typo then the quadratic equation yields:
x = {9.568, -1.568}
Details of quadratic equation follows:
.
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation (in our case ) has the following solutons:



For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=124 is greater than zero. That means that there are two solutions: .




Quadratic expression can be factored:

Again, the answer is: 9.56776436283002, -1.56776436283002. Here's your graph:
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