1=(m-n)(m+n)-mn(m+n)=(m+n)(m-n-mn)
2.=x²+y²-2xy+3x²-3y²-4x²-4y²+8xy=6xy-6y²=6y(x-y)
3.
4.
5.=(x-2)(x-1)(x²+ax+b)=(x²-3x+2)(x²+ax+b)=x^4+(a-3)x³+(2+b-3a)x²+(2a-3b)x+2b
所以2b=16; 2a-3b=0 2+b-3a=n a-3=m
算出b=8; a=12; n=-26; m=9
6.(x-a-b)/c +( x-b-c)/a + (x-c-a)/b =3
(1/c+1/a+1/b)x-[(a+b)/c +( b+c)/a + (c+a)/b]=3
(1/c+1/a+1/b)x=(a+b)/c+1 +( b+c)/a +1+ (c+a)/b+1=(a+b+c)(1/c+1/a+1/b)
x=a+b+c
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