SOLUTION: What are all possible values of b if 2x^2 +bx= -8 has a discriminant of -15 ? I said 7 but I got it wrong. I don't know how to solve this , can someone please help me ?

Question 118655: What are all possible values of b if 2x^2 +bx= -8 has a discriminant of -15 ? I said 7 but I got it wrong. I don't know how to solve this , can someone please help me ?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!

What are all possible values of b if 2x^2 + bx = -8 has a discriminant of -15 ?
:
Put equation in the: y = ax^2 + bx + c; form
:
I think you know how to solve it, you just forgot 1 little thing:
:
y = 2x^2 + bx + 8
:
a = 2; c = 8; find b
:
The discriminant: b^2 - 4*a*c
In this problem
b^2 - (4 * 2 * 8) = -15
:
b^2 - 64 = -15
:
b^2 = -15 + 64
:
b = +/-Sqrt(49)
:
b = +/-7 (plus or minus 7 is probably what they wanted you to say.)
:
you can see that 7^2 and -7^2 will have the same value for b^2
:
y = 2x^2 + 7x + 8
and
y = 2x^2 - 7x + 8
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