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\(\left(a+b-c\right)^2-\left(a-c\right)^2-2ab-2bc=\left(a+b-c-a+c\right)\left(a+b-c+a-c\right)-2b\left(a+c\right)\)
\(=b\left(2a+b-2c\right)-b\left(2a+2c\right)\)
\(=b\left(2a+b-2c-2a-2c\right)=b\left(b-4c\right)\)
\(\left(a+b-c\right)^2-\left(a-c\right)^2-2ab-2bc\)
\(=\left(a+b\right)^2-2.\left(a+b\right).c+c^2-a^2+2ac-c^2-2ab-2bc\)
\(=a^2+2ab+b^2-2ac-2bc+c^2-a^2+2ac-c^2-2ab-2bc\)
\(=b^2-4bc\)
\(=b\left(b-4c\right)\)
(a+b-c)2-(a-c)2-2ab-2bc
=a2+ b2+ c2+ 2ab- 2bc- 2ca- a2+ 2ac- c2- 2ab- 2bc
=b2-4bc
=b.(b-4c)
\(\left(a+b\right)\left(a^2-b^2\right)+\left(b+c\right)\left(b^2-c^2\right)+\left(c+a\right)\left(c^2-a^2\right)\)
\(=\left(a+b\right)\left(a^2-b^2\right)-\left(b+c\right)\left[c^2-a^2+a^2-b^2\right]+\left(c+a\right)\left(c^2-a^2\right)\)
\(=\left(a+b\right)\left(a^2-b^2\right)-\left(b+c\right)\left(c^2-a^2\right)-\left(b+c\right)\left(a^2-b^2\right)+\left(c+a\right)\left(c^2-a^2\right)\)
\(=\left(a^2-b^2\right)\left(a+b-b-c\right)+\left(c^2-a^2\right)\left(c+a-b-c\right)\)
\(=\left(a-b\right)\left(a+b\right)\left(a-c\right)+\left(c-a\right)\left(c+a\right)\left(a-b\right)\)
\(=\left(a-b\right)\left(a-c\right)\left(a+b-c-a\right)\)
\(=\left(a-b\right)\left(a-c\right)\left(b-c\right)\)
Chúc bạn học tốt.
\(a\left(b^2+c^2\right)+b\left(a^2+c^2\right)+c\left(a^2+b^2\right)+2abc\)
\(=ab^2+ac^2+ba^2+bc^2+ca^2+cb^2+2abc\)
\(=\left(ab^2+ba^2\right)+\left(ac^2+bc^2\right)+\left(ca^2+abc\right)+\left(cb^2+abc\right)\)
\(=ab\left(a+b\right)+c^2\left(a+b\right)+ca\left(a+b\right)+cb\left(a+b\right)\)
\(=\left(a+b\right)\left(ab+c^2+ca+cb\right)\)
\(=\left(a+b\right)\left(a+c\right)\left(b+c\right)\)
hình như cộng 2abc chứ sao +2ab