2X2+3X=20 Complete the square

Question

Solve by completing the square. The Number two after the X is squared. I know the answer is x=-4 or X=5/2 could you please show how to get that.

Answer 1

Hi Roseland,

 

2x²+3x=20

 

2x²+3x-20=0

 

2x²+8x-5x-20=0

 

2x(x+4)-5(x+4)=0

 

(2x-5)(x+4)=0

 

2x-5=0  or  x+4=0

2x=5          x=-4

 

x=5/2 or x=-4

Answer 2

Hi Roseland;

2X²+3X=20

2x²+3x-20=0

 

For the FOIL...

FIRST must be (2x)(x)=2x²

OUTER and INNER must add-up to 3x

LAST must be (5)(4) or (4)(5) or (10)(2) or (2)(10) or (20)(1) or (1)(20) and only one number must be negative to render the sum of +3 and product of -20.

(2x-5)(x+4)=0

Let's FOIL...

FIRST..(2x)(x)=2x²

OUTER...(2x)(4)=8x

INNER...(-5)(x)=-5x

LAST...(-5)(4)=-20

2x²+8x-5x-20=0

2x²+3x-20=0

(2x-5)(x+4)=0

Either or both parenthetical equation(s) must equal zero...

2x-5=0, 2x=5, x=5/2

x+4=0, x=-4

THESE ARE YOUR RESULTS.