(ax+by+c)(dx+ey+f)
=adx^2+(ae+bd)xy+bey^2+(af+cd)x+(bf+ce)y+cf
ad=3.①
ae+bd=5.②
be=-2.③
af+cd=1.④
bf+ce=9.⑤
cf=-4.⑥
3b^2-2a^2=5ab.1)
4b^2+2c^2+9bc=0.2)
3c^2-4a^2=ac.3)
慢慢解吧