3x(2x-7)=5x²
6x²-21x=5x²
移项得6x²-5x² -21x=0
x²-21x=0
x(x-21)=0
2(x+3)²=3x+16
2(x²+6x+9)=3x+16
展开,移项得2x²+9x+2=0