SOLUTION: 2x squared + 10x = -1

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Question 116121: 2x squared + 10x = -1
Found 2 solutions by bucky, jim_thompson5910:
Answer by bucky(2189) About Me  (Show Source):
You can put this solution on YOUR website!
Let's begin this problem by getting it into the standard quadratic form:
.
ax%5E2+%2B+bx+%2B+c+=+0
.
You can get it into the quadratic form by adding 1 to both sides of the equation to transform it
to:
.
2x%5E2+%2B+10x+%2B1+=+0
.
By comparing this to the standard form above you can see that "a" corresponds to 2,
b corresponds to 10, and c corresponds to 1.
.
If you have trouble factoring the original problem or you suspect that the problem may have a
set of complex answers, a good method to use on a quadratic equation is the quadratic formula
which says that for the form:
.
ax%5E2+%2B+bx+%2B+c+=+0
.
the solution is given by:
.
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
.
for this problem, if you substitute +2 for a, +10 for b, and +1 for c, you get the solution
as:
.
x+=+%28-%2810%29+%2B-+sqrt%28+10%5E2-4%2A2%2A1+%29%29%2F%282%2A2%29+
.
Inside the radical sign the 10%5E2+-+4%2A2%2A1 simplifies to 100+-+8+=+92. Since this is
positive you know that the two values of x will be real. The square root of 92 is 9.591663047.
Substituting this into the equation for x results in:
.
x+=+%28-%2810%29+%2B-+9.591663047%29%2F%282%2A2%29+
.
The -(10) is equivalent to -10 and in the denominator the 2*2 = 4. These two simplify the
equation for x to:
.
x+=+%28-10+%2B-+9.591663047%29%2F4
.
This means the two answers for x are:
.
x+=+%28-10+%2B+9.591663047%29%2F4+=+-0.408336953%2F4+=+-0.102084238
.
and
.
x+=+%28-10+-+9.591663047%29%2F4++=+-19.591663047%2F4+=+-4.897915762
.
Hope this helps you to do the problem. If you want to get the answers in terms of radicals,
you can replace sqrt%2892%29 by 2%2Asqrt%2823%29 and your answers will be:
.
x+=+%28-%2810%29+%2B-+2%2Asqrt%2823%29%29%2F%282%2A2%29+
.
Which you can simplify down to:
.
x+=+%28-5%2B-sqrt%2823%29%29%2F2
.

Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

2x%5E2%2B10x=-1 Start with the given equation


2x%5E2%2B10x%2B1=0 Move all of the terms to the left side

Let's use the quadratic formula to solve for x:


Starting with the general quadratic

ax%5E2%2Bbx%2Bc=0

the general solution using the quadratic equation is:

x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29



So lets solve 2%2Ax%5E2%2B10%2Ax%2B1=0 ( notice a=2, b=10, and c=1)




x+=+%28-10+%2B-+sqrt%28+%2810%29%5E2-4%2A2%2A1+%29%29%2F%282%2A2%29 Plug in a=2, b=10, and c=1



x+=+%28-10+%2B-+sqrt%28+100-4%2A2%2A1+%29%29%2F%282%2A2%29 Square 10 to get 100



x+=+%28-10+%2B-+sqrt%28+100%2B-8+%29%29%2F%282%2A2%29 Multiply -4%2A1%2A2 to get -8



x+=+%28-10+%2B-+sqrt%28+92+%29%29%2F%282%2A2%29 Combine like terms in the radicand (everything under the square root)



x+=+%28-10+%2B-+2%2Asqrt%2823%29%29%2F%282%2A2%29 Simplify the square root (note: If you need help with simplifying the square root, check out this solver)



x+=+%28-10+%2B-+2%2Asqrt%2823%29%29%2F4 Multiply 2 and 2 to get 4

So now the expression breaks down into two parts

x+=+%28-10+%2B+2%2Asqrt%2823%29%29%2F4 or x+=+%28-10+-+2%2Asqrt%2823%29%29%2F4


Now break up the fraction


x=-10%2F4%2B2%2Asqrt%2823%29%2F4 or x=-10%2F4-2%2Asqrt%2823%29%2F4


Simplify


x=-5+%2F+2%2Bsqrt%2823%29%2F2 or x=-5+%2F+2-sqrt%2823%29%2F2


So these expressions approximate to

x=-0.10208423834364 or x=-4.89791576165636


So our solutions are:
x=-0.10208423834364 or x=-4.89791576165636

Notice when we graph 2%2Ax%5E2%2B10%2Ax%2B1, we get:



when we use the root finder feature on a calculator, we find that x=-0.10208423834364 and x=-4.89791576165636.So this verifies our answer