Loading [MathJax]/jax/output/SVG/jax.js
 
+0  
 
0
732
5
avatar

How do you solve 2x^2 + 6x - 5 = 0 ? I divided by 2 to get x^2 + 3x - 2.5, but I can't find two numbers that add to equal 3 and multiply to equal -2.5

 Feb 9, 2016

Best Answer 

 #4
avatar+33654 
+5

Divide by 2 first and take constant to the RHS:  x2+3x=52

 

Now add square of half the coefficient of x to both sides:  x2+3x+94=52+94

 

Rewrite as:  (x+32)2=194

 

You should be able to take it from here.

 Feb 9, 2016
 #1
avatar
0

Remeber the 'Quadratic Formula' ???   Use it.....

 Feb 9, 2016
 #2
avatar
+5

Nope

Nobody said anything about a formula unless you mean "Take half he coefficient of x and square it and add it to both sides"

Do you do that before or after dividing by 2?

 Feb 9, 2016
 #3
avatar+2499 
+5

let s use (a+b)2=a2+2ab+b2 and a2b2=(ab)(a+b):x2+3x2.5=0x2+3x2.5+4.75=0+4.75x2+3x+2.25=4.75 (1.5*1.5=2.25 1.5*2=3x)(x+1.5)2=4.75(x+1.5)24.75=0(x+1.54.75)(x+1.5+4.75)=0x1=0.679449x2=3.67945

.
 Feb 9, 2016
edited by Solveit  Feb 9, 2016
 #4
avatar+33654 
+5
Best Answer

Divide by 2 first and take constant to the RHS:  x2+3x=52

 

Now add square of half the coefficient of x to both sides:  x2+3x+94=52+94

 

Rewrite as:  (x+32)2=194

 

You should be able to take it from here.

Alan Feb 9, 2016
 #5
avatar
0

FOLLOW THE PROCEDURE OUTLINED IN THIS SOLUTION:

 

Solve for x:

2 x^2+6 x-5 = 0

Divide both sides by 2:

x^2+3 x-5/2 = 0

Add 5/2 to both sides:

x^2+3 x = 5/2

Add 9/4 to both sides:

x^2+3 x+9/4 = 19/4

Write the left hand side as a square:

(x+3/2)^2 = 19/4

Take the square root of both sides:

x+3/2 = sqrt(19)/2 or x+3/2 = -sqrt(19)/2

Subtract 3/2 from both sides:

x = sqrt(19)/2-3/2 or x+3/2 = -sqrt(19)/2

Subtract 3/2 from both sides:

Answer: |x = sqrt(19)/2-3/2                or x = -3/2-sqrt(19)/2

 Feb 9, 2016

1 Online Users

avatar