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2: =abc-bc-ab-ac+a+b+c-1
=bc(a-1)-ab+b-ac+c+a-1
=bc(a-1)-b(a-1)-c(a-1)+(a-1)
=(a-1)(bc-b-c+1)
=(a-1)(b-1)(c-1)
Ta có: \(D=ab\left(a+b\right)+bc\left(b+c\right)+ca\left(c+a\right)+3abc\)
\(=a^2b+ab^2+b^2c+bc^2+ac^2+a^2c+3abc\)
\(=\left(a+b\right)\left(b+c\right)\left(a+c\right)\)
Co P=ab(a-b) + bc((b-a)+(a-c)) +ac(c-a)
=ab(a-b) -bc(a-b) -bc(c-a) +ac(c-a)
=(a-b)(ab-bc) +(c-a)(ac-bc)
=(a-b) b (a-c) + (c-a) c (a-b)
=(a-b)(a-c)(b-c)
sửa đề thành \(ab\left(a+b\right)+bc\left(b+c\right)+ca\left(c+a\right)+2abc\)
\(=ab\left(a+b\right)+b^2c+bc^2+c^2a+ca^2+2abc\)
\(=ab\left(a+b\right)+\left(b^2c+abc\right)+\left(c^2a+c^2b\right)+\left(a^2c+abc\right)\)
\(=ab\left(a+b\right)+bc\left(a+b\right)+c^2\left(a+b\right)+ac\left(a+b\right)\)
\(=\left(a+b\right)\left(ab+bc+a^2+ca\right)\)
\(=\left(a+b\right)\left[\left(ab+bc\right)+\left(c^2+ac\right)\right]\)
\(=\left(a+b\right)\left[b\left(a+c\right)+c\left(c+a\right)\right]\)
\(\left(a+b\right)\left(b+c\right)\left(c+a\right)\)
= (abc - ab) + (a - ca) + (b - bc) + (c -1) = ab.(c -1) - a.(c - 1) - b(c -1) + (c -1) = (c -1).(ab - a - b + 1)
abc-(ab+bc+ca)+(a+b+c)-1
=abc-ab-bc-ca+a+b+c-1
=(abc-ab)+(-bc+b)+(-ca+a)+(c-1)
=ab.(c-1)-b.(c-1)-a.(c-1)+(c-1)
=(c-1)(ab-b-a+1)
=(c-1)[b.(a-1)-(a-1)]
=(c-1)(a-1)(b-1)
bc(b+c)+ca(c-a)-ab(a+b)
=bc(b+c)+ca(b+c)-ca(a+b)-ab(a+b)
=c(a+b)(b+c)-a(a+b)(b+c)
=(c-a)(a+b)(b+c)