3x+x（14-5-x）=19
3x+x（9-x）=19
3x+9x-x^2=19
12x-x^2=19
x^2-12x+19=0
x^2-12x+36-36+19=0
(x-6)^2-17=0
(x-6-√17)(x-6+√17)=0
x=6+√17或x=6-√17