作业帮上面8,9两题,
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上面8,9两题,
上面8,9两题,
上面8,9两题,
8 =[5(a+b)+4(a-b)][5(a+b)-4(a-b)]=(9a+b)(a+9b)
9 =[0.5(x+y)+0.9(x-y)][0.5(x+y)-0.9(x-y)]=(1.4x-0.4y)(1.4y-0.4x)=0.04(7x-2y)(7y-2x)
8、
25(a+b)²-4(a-b)²
=(5a+5b)²-(2a-2b)²
=(5a+5b+2a-2b)(5a+5b-2a+2b)
=(7a+3b)(3a+7b)
9、
0.25(x+y)²-0.81(x-y)²
=(0.5x+0.5y)²-(0.9x-0.9...
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8、
25(a+b)²-4(a-b)²
=(5a+5b)²-(2a-2b)²
=(5a+5b+2a-2b)(5a+5b-2a+2b)
=(7a+3b)(3a+7b)
9、
0.25(x+y)²-0.81(x-y)²
=(0.5x+0.5y)²-(0.9x-0.9y)²
=(0.5x+0.5y+0.9x-0.9y)(0.5x+0.5y-0.9x+0.9y)
=(1.4x-0.4y)(-0.4x+1.4y)
=0.16(3.5x-y)(3.5y-x)
=0.04(7x-2y)(7y-2x)
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