$ 解:因为原来的两位数为10(x-2)+x=10x-20+x=11x-20$ $新的两位数为10x+(x-2)=10x+x-2=11x-2$ $所以新数比原数大(11x-2)-(11x-20)=11x-2-11x+20=18$ $ 即新数比原数大18$ $-\frac{2x^{2}y^{2}}{5},0,-9x^{2}$ $a^{2}x+ax^{2},\frac27+3x-y^{2},\frac{a-b}{2},\frac{x}{5}+\frac{y}{2}-3xy$ $a^{2}x+ax^{2},\frac27+3x-y^{2},-\frac{2x^{2}y^{2}}{5},0,-9x^{2},\frac{a-b}{2},\frac{x}{5}+\frac{y}{2}-3xy$ $a^{2}x+ax^{2},\frac{a-b}{2}$ $\frac27+3x-y^{2},\frac{x}{5}+\frac{y}{2}-3xy$
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