Factorise 3x^2 + 5x - 12?

(3x-4)(x+3)
---solving for x
3x-4=0 and x+3=0
therefore
x=4/3 and -3

(3x - 4)(x + 3)

3x^2 +9x-4x -12=0
3x( x +3) -4(x +3)=0
(3x-4) (x+3)=0.
3x-4=0, 3x=4, x= 4/3.
x+3=0, x= -3.
Ans... x=4/3, -3.

3x^2 + 5x - 12
= (3x - 4)(x + 3)

3x^2 + 5x - 12= (3x - 4)(x + 3)

just use the formula
X = -b+-root (b^2-4ac)/2a

=3x^2 + (9-4)x -12

3x( x+3) -4(x+3)

(3x-4) (x+3)

x=-3; 4/3

3x^2+5x-12
=3x^2+9x-4x-12
=3x(x+3)-4(x+3)
=(x+3)(3x-4)
thats it..