单复句子互换This is my brother This is his cousinThese are ID card

我是个高中生,下面为你解答
These are my brothers
These are his cousins
This is ID card
That is baseball
Are these your fathers? 很简单的
下面是数学
X-[Y-2X-(X-Y)]=X-Y+2X+(X-Y)=X-Y+2X+X-Y=4X-2Y 注意式子钱为-要加变减 减变加 +则不用 照抄就行
2(a2b-3ab2)-3(2a2b-7ab2)=2a2b-6ab2-6a2b+21ab2=15ab2-4a2b=还可以把ab提出来=ab（15b-4a）
m2与-2n2的和为A ∴A=m2-2n2 1+n2与-2m2的差为B ∴ B=1+n2+2m2
2A-4B=2（m2-2n2）-4（1+n2+2m2）=-6m2-4n2-4
4X2Y-{6xy-3（4xy-2）-x2y｝+1=3x2y+6xy-5 又x=2 y=? ∴原式=6+6-5=7
最后一题 设原来的多项式为A ∴A+x2+6x-6=2x2-2x+3 A=x2-8x+9
∴A-（x2+6x-6）=x2-8x+9-x2-6x+6=15-14x