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

单复句子互换
This is my brother
This is his cousin
These are ID card
Those are baseballs
Is yhis your faher?
X-[y-2x-(x-y)}
2(a²b-3ab²)-3(2a²b-7ab²)
一直m²与-2n²的和为A,1+n²与-2m²的差为B,求2A-4B
先化简再求值：4X²Y-{6xy-3（4xy-2）-x²y｝+1其中x=2,y=二分之一
由于看错了符号,某学生把一个多项式减去x²+6x-6误当成了加法计算,结果得到2x²-2x+3,正确的结果应该是多少?

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