(x+3)(x+4)=30
x^2+7x+12=30
x^2+7x+12-30=0
x^2+7x-18 =0
(x+9)(x-2)=0
x+9=0 or x-2=0
x=-9 x=2
x=-9 , 2
将(x+3)(x+4)=30用因式分解法解二元一次方程,
(x+3)(x+4)=30
x^2+7x+12=30
x^2+7x+12-30=0
x^2+7x-18 =0
(x+9)(x-2)=0
x+9=0 or x-2=0
x=-9 x=2
x=-9 , 2