Equations (maths)

Question

"Solve the equation 3x^2+4x-12=0

Give your solution to 2 decimal places"

 

I would like to know how to workout this, as I only have the answer.

 

thank you.

Answer 1

COMPLETING THE SQUARE

3x² +4X-12=0

 

3x² +4X-12=0

       3

x² +4X-4=0

        3

 

x² +  4X   +  (4/6 )²    -    (4/6 )² -  4=0
        3

 

(X+ 4/6 )²      -    (4/6 )² -  4=0

 

(X+ 4/6 )² =   (4/6 )²+ 4

 

√(X+ 4/6 )²= √ (4/6 )²   + 4

 

(X+ 4/6 ) = 2.10

 

X=   2.10-4/6

 X = 1.43

 

 

 

Answer 2

For an equation like aX² + bX +c =0, the solutions are 

 

x= [-b ± sqrt(b² -4ac)]/ 2a

 

Thus, the roots are 1.44 and -2.77