Question

Solve: 0 = 4x2 − 8x − 5.
x=-1/2,x=5/2
x=1/2,x=-5/2
x=1/2,x=-5/2
x=1/2,x=5/2

Answer 1

Do you know how to factor by grouping?

Answer 2

dont i have to multiply the 4 and 8 and the substrac the 2 by the x?

Answer 3

No. Find factors of -20 that add up to -8.

Answer 4

-28

Answer 5

How is -28 a factor of -20 and how does it add to -8?

Answer 6

You're not supposed to add them.

Answer 7

0 = 4x^2 - 8x - 5
0 = 4x^2 - 10x + 2x - 5
0 = 2x(2x - 5) + (2x - 5)
0 = (2x + 1)(2x - 5)
Can you solve for x from here?

Answer 8

http://www.algebra.com/algebra/homework/quadratic/Quadratic_Equations.faq.question.184643.html
it might help