SOLUTION: x2+4x-21=0 trying to find the two solutions??? I was fine till c was a value... when c = o I had no problems solving now that c = a value.. im stuck help i can get this far: a

Question 139775: x2+4x-21=0
trying to find the two solutions??? I was fine till c was a value... when c = o I had no problems solving now that c = a value.. im stuck help i can get this far:
a=1
b=4
c= -21 -4+_ 4sqd + 4(1)(-21) divided by 2(1)

then, -4+- 4sqd + -84 divided by 2
then i get confused.... help

Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Let's use the quadratic formula to solve for x:

Starting with the general quadratic

the general solution using the quadratic equation is:

So lets solve ( notice , , and )

Plug in a=1, b=4, and c=-21

Square 4 to get 16

Multiply to get

Combine like terms in the radicand (everything under the square root)

Simplify the square root (note: If you need help with simplifying the square root, check out this solver)

Multiply 2 and 1 to get 2

So now the expression breaks down into two parts

or

Lets look at the first part:

Add the terms in the numerator
Divide

So one answer is

Now lets look at the second part:

Subtract the terms in the numerator
Divide

So another answer is

So our solutions are:
or

Notice when we graph , we get:

and we can see that the roots are and . This verifies our answer

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