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Question

Solve 2 x2 + x = 15 using the quadratic formula.

Im sorry its 2x^2+x=15

Multiple Choice:

3/5, -15

5/2,-3

15/2,-1

5/3,-2

Answer 1

Hi Dear Porita ;

2 x^ 2 + x = 15

2 x^ 2 + x - 15 =0

if a = 2 , b = 1 & c = -15
∆ = b ^2 - 4ac
∆ = ( 1 ^2 ) - 4 ( 2)(-15) = 1 + 120 = 121

x 1 = ( -b + √ ∆ ) / 2a = (-(1) + √ 121) / 4 = -1 +11 / 4 = 10/4 = 2.5
x 2 = ( -b - √ ∆ ) / 2a = (-(1) - √ 121) / 4 = -1 111 / 4 = -12/4 =
-3

x1 = 2.5
x2 = -3

Good Luck Dear.

Answer 2

Mariko is right. But you wanted the solution using the quadratic formula?

x = (-b +- sqrt(b^2 - 4ac))/2a
In this case, a = 2, b = 1, c = -15

Just plug in the values and go from there
x = (-1 +- sqrt(1 - 4(2)(-15)))/4
= (-1 +- sqrt(1 - (-120))/4
= (-1 +- sqrt(121))/4
= (-1 +- 11) / 4
= -12/4 or 10/4
= -3 or 5/2

Answer 3

To solve this you must factor.

2x^2 +x-15=0 Subtract 15 from both sides
(2x - 5)(x + 3) = 0 Factoring

This equation is true when either
2x - 5 = 0
or
x + 3 = 0

So your answers are x = 5/2 and -3

Answer 4

Put it in general form"

2x^2 + x -15 = 0

a=2, b=1, c=-15

Plug into the quadratic formula:

x = (-b +-√(b^2-4ac))/2a

You should get -3 and 5/2 as the answer.

Mariko got the right answer but used the wrong technique. Other people used the right technique but miscalculated.

b^2-4ac = 1+120 = 121

√(121) = 11.

I'll let you work the rest out yourself...

Answer 5

subtract 15 to the other side so you have 2x^2+x-15=0
Then let 2=a 1=b -15=c
the quadratic formula is -b plus/minus the square root of b^2-4ac divided by 2a

This will give you answers of 5 and -6

Answer 6

2x^2 +x =15
2x^2 +x-15=0
2x^2 +6x-5x-15=0 ; so now
(2x^2 +6x) - (5x+15) =0 ; now take out common factor
so, 2x(x+3) -5(x+3)=0 ; now we can write this term as
(x+3) (2x-5) =0
x+3=0 and 2x-5=0
x= -3 2x = 5
x= 5/2

Ans. x= -3, 5/2

Answer 7

To use the quadratic formula your equation has to equal zero.
Change it to 2x^2 + x - 15 = 0

In your formula, a = 2, b = 1 and c = -15

x = [-1 +/- square root (1+ 60)]/4
= [-1 +/- square root 61]/4

Answer 8

2 x^2 + x = 15
First subtract 15 from both sides
2x ^2 + x - 15 = 0
(2x - 3)(x + 2 )=0
So either 2 x - 3 = 0 or x + 2 = 0
2x -3 = 0
2x = 3
x = 3/2

or x + 2 = 0
x = -2

Answer 9

2x^2 + x = 15
2x^2 + x - 15= 0
(x + 3)(2x-5) = 0
x + 3 = 0 or 2x - 5 = 0
x = -3 or x = 5/2

Answer 10

easy...

2x^2 + x - 15 = 0
(2x-5)(1x+3) = 0
2x-5 = 0 or x+3=0
2x = 5 x=-3
x =2.5

Answer= x=2.5 or x= -3


working:
2x -5 | -5x
1x +3 | +6x
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