SOLUTION: 2x^2-x-21=0... solve by factoring,completing the square, and the quadratic formula. thanks in advance.

Question 453386: 2x^2-x-21=0... solve by factoring,completing the square, and the quadratic formula.
thanks in advance.
Answer by rwm(914) (Show Source): You can put this solution on YOUR website!
complete the square
(x-1/4)^2=169/4
factor
factors of -42 which add up to -1
-7 and 6
2x^2+6x-7x-21=0
2x*(x+3)-7*(x+3)=0
(x+3)*(2x-7) = 0
quadratic formula

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=169 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 3.5, -3. Here's your graph:

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