7年级的数学题

1.
4-(X+2)(X-2)
=4-(X²-4)
=4-X²+4
=8-X²

2.若A^MB^3与-1/2AB^M-N能合并同类项,
则A^M=A,B^3=B^(M-N)
M=1,M-N=3
M=1,N=-2
M^2+N^2=1+4=5

3.若25X^2+MXY+9Y^2能利用完全平方公式,则M=
25X²+MXY+9Y²
=(5X)²+30XY+(3Y)²-30XY+MXY
=(5X+3Y)²+(M-30)XY
M-30=0
M=30

4.用科学记数法表示:
3 102 000= 3.102*10^6
0.000 000 108= 1.08*10^(-7)

5.(-0.25)^2008*4^2007
=0.25^2008*4^2007
=0.25*(0.25*4)^2007
=0.25

6.已知(A-B)^2=1,且A^2+B^2=4,则
2AB=A²+B²-(A-B)²
=4-1=3

7.计算:
(2X+3Y-1)(2X-3Y+1)
=[2X+(3Y-1)][2X-(3Y-1)]
=4X²-(3Y-1)²
=4X²-(9Y²-6Y+1)
=4X²-9Y²+6Y-1

1.计算4-(X+2)(X-2)= 4-X^2+4=8-x^2

2.若A^MB^3与-1/2AB^M-N能合并同类项,则M^2+N^2= 5

3.若25X^2+MXY+9Y^2能利用完全平方公式,则M= 30

4.用科学记数法表示:
3 102 000= 3.102*10^6
0.000 000 108= 1.08*10^-7

5.(-0.25)^2008乘4^2007= 0.25

6.已知(A-B)^2=1,且A^2+B^2=4,则2AB= 3

7.计算:(2X+3Y-1)(2X-3Y+1)
=[2X+(3Y-1)][2X-(3Y-1)]
=4X^2-(3Y-1)^2
=4X^2-9Y^2+6Y-1