Have a math prob, I am stuck on?

Question

Ok I know how to simplify things but this one I can't do... its
x^2+2x-5

I know that normally you multiply the first number which will be 1 in this case, by the last which is neg 5 and u get neg 5...then you have to factor it to find 2 numbers that add together to give you the middle number...2, but I can't figure it out...seems impossible...this is just a tiny part of a huge problem Im working on...PLEASE HELP ASAP

Thanks, well can you simplify 4x? is it 2(2x) or does that even count as simplifying?

Answer 1

this one (and most non-trivial ones) is easist by completing the square

x^2 + 2x - 5 = (x+1)^2 - 6 = (x+1+sqrt(6))(x+1-sqrt(6))

Answer 2

When I see an equation of form x^2 + bx + c, I like to complete the square by adding (b/2)^2 and then subtracting it:

x^2 + 2x - 5 = x^2 + 2x + 1 -1 - 5 = (x + 1)^2 - 6 =

= [x + 1 - sqrt(6)][x + 1 + sqrt(6)]

because a^2 - b^2 = (a - b)(a + b) with a=x+1 and b=sqrt(6)

Answer 3

In cases like this, it's helpful to learn (and do) the quadratic equation.

Learn a little about the quadratic equation here:
http://mathworld.wolfram.com/QuadraticEquation.html

It's point number five, about a quarter of the way down the page.

The quadratic equation gives you two possible answers for x.
The variable a is the number multiplied by x^2 (here, it's 1).
The variable b is the number multiplied by x (here, it's 2)
the variable c is the number not multiplied by x (here, it's negative five).

Answer 4

factoring just wont work here.

You have to use the quadratic formula if you need to solve it.

http://en.wikipedia.org/wiki/Quadratic_formula#Quadratic_formula

for this problem a = 1 b =2 and c = -5 for the quadratic formula.

x = [-2 +/- sqrt(2^2 - 4(1)(-5))]/2(1)
= [-2 +/- sqrt(24)]/2 = -1 +/- sqrt(6)
x = 1.449 or -3.449

Answer 5

Quadtatic Formula

x = - b ± √b² - 4ac / 2a

x² + 2x - 5

a = 1

b = 2

c = - 5

x = - 2 ± √(2)² - 4(1)(- 5) / 2(1)

x = - 2 ± √4 - ( -24) / 2

x = - 2 ± √4 + 24 / 2

X = - 2 ± √28 / 2

X = - 2 ± 5.291502622 / 2

-- - - - - - - -

Solving for +

x = - 2 + 5.292502622 / 2

x = 3.291502622 / 2

x = 1.64571311

- - - - - - - - - -

Solving for -

x = - 2 - 5.291502622 / 2

x = - 7.291502622 / 2

x = - 3.645751311

- - - - - - - s-

Answer 6

maybe you should use the quadratic equation...
-b+/- square root of b^2 +4ac all over 2a, a=1, b=2, c=-5

if that's not it, then check the rest of the problem you've been working on; maybe you made a mistake. if that's not the case, then sorry, i really don't know what to do!!

Answer 7

Have you learned the quadratic equation?

[ -b +/- SQRT(b^2 - 4(a)(c) ) ]/ 2a

So in your equation, x^2+2x-5

a= 1
b= 2
c= -5

Sub in the a,b,c


[ -2 +/- SQRT{ (-2)^2 - 4(1)(-5) } ]/ 2(1)

Then it comes to

[ -2 +/- SQRT{24} ] / 2

So the two answers are,

[ -2 + SQRT{24} ] / 2
and
[ -2 - SQRT{24} ] / 2

So x= 1.45 and x= -3.45

Answer 8

use the quadratic formula, its not a simple factor problem

Answer 9

ok. wat u need to do is.... use the quadratic formula... hopefully you know it, b/c i can't insert a pic of it. it is something like...

x= -b +/- (the square root of b^2 - 4ac)
----------------------------------------------
2a

sorry if it is kind of messy, but u get the general idea. anyways, in this equation, you substitute...
a=1
b=2
and c= -5

now try and simplify it by plugging in the numbers

Answer 10

I believe you will have to use the quadratic formula