3x^2+10x-8=0
3x^2+10x=8
3(x^2 + (10/3)x + (5/3)^2 ) = 8 + 25/3
3(x^2 + (10/3)x + (5/3)^2 ) =49/3
3(x+ 5/3)^2 =49/3