9(x-y)^2+42(x-y)+49 16(x+y)2+40(x+y)(x-y)+25(x-y)^2 你懂的……没分了= =谅解..

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9(x-y)^2+42(x-y)+49 16(x+y)2+40(x+y)(x-y)+25(x-y)^2 你懂的……没分了= =谅解..
9(x-y)^2+42(x-y)+49 16(x+y)2+40(x+y)(x-y)+25(x-y)^2 你懂的……没分了= =谅解..

9(x-y)^2+42(x-y)+49 16(x+y)2+40(x+y)(x-y)+25(x-y)^2 你懂的……没分了= =谅解..
9(x-y)^2+42(x-y)+49
=[3(x-y)]^2+2*3(x-y)*7+7^2
= [3(x-y)+7]^2
= (3x-3y+7)^2
16(x+y)2+40(x+y)(x-y)+25(x-y)^2
=[4(x+y)]^2+2*4(x+y)*5(x-y)+[5(x-y)]^2
=[4(x+y)+5(x-y)]^2
=(4x+4y+5x-5y)^2
=(9x-y)^2