例题：已知9-6y-4y^2=7,求2y^2+3y+7的值.
问题描述：
例题：已知9-6y-4y^2=7,求2y^2+3y+7的值.
答
9-6y-4y^2=7
-6y-4y^2=7-9
6y 4y^2=2
2y^2 3y 7
=3y 2y^2 7
=2/1(6y 4y^2) 7
=1 7
=8