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\(ab\left(a+b\right)+bc\left(b+c\right)+ca\left(c+a\right)+2abc\)
\(=ab\left(a+b\right)+abc+bc\left(b+c\right)+abc+ca\left(c+a\right)\)
\(=ab\left(a+b+c\right)+bc\left(b+c+a\right)+ca\left(c+a\right)\)
\(=\left(a+b+c\right)\left(ab+bc\right)+ca\left(c+a\right)\)
\(=b.\left(a+b+c\right)\left(a+c\right)+ca\left(c+a\right)\)
\(=\left(a+c\right)\left[b.\left(a+b+c\right)+ca\right]\)
\(=\left(a+c\right)\left(ab+b^2+bc+ca\right)\)
\(=\left(a+c\right)\left[a\left(b+c\right)+b\left(b+c\right)\right]\)
\(=\left(a+c\right)\left(b+c\right)\left(a+b\right)\)
\(ab\left(a+b\right)+bc\left(b+c\right)+ca\left(c+a\right)+3abc\)
\(=ab\left(a+b\right)+abc+bc\left(b+c\right)+abc+ca\left(c+a\right)+abc\)
\(=ab\left(a+b+c\right)+bc\left(b+c+a\right)+ca\left(c+a+b\right)\)
\(=\left(a+b+c\right)\left(ab+bc+ac\right)\)
Tham khảo nhé~
phân tích bằng đặt ẩn phụ=))
Ta có:\(\left(a^2+b^2+c^2\right)\left(a+b+c\right)^2+\left(ab+bc+ca\right)^2\)
\(=\left(a^2+b^2+c^2\right)\left[\left(a^2+b^2+c^2\right)+2\left(ab+bc+ca\right)\right]+\left(ab+bc+ca\right)^2\)
Đặt:\(a^2+b^2+c^2=x;ab+bc+ca=y\),ta có:
\(x\left(x+2y\right)+y^2=x^2+2xy+y^2=\left(x+y\right)^2\)
Thay vào,ta được:\(\left(x+y\right)^2=\left(a^2+b^2+c^2+ab+bc+ca\right)^2\)
(x^2-x+2)^2+(x-2)^2
= [(x^2-x+2)+(x-2)]^2-2[(x^2-x+2)*(x-2)] (áp dụng (a^2+b^2)=(a+b)^2-2ab
=(x^2)^2- 2((x^3-3x^2+4x-4)
=x^4-2x^3+6x^2-8x+8
giờ phân tích đa thức
x^4-2x^3+6x^2+8x-8
=(x^4-2x^3+2x^2)+(4x^2-8x+8) (cái này làm bài tập nhiêu nhìn ra nhanh)
=[x^2(x^2-2x+2)]+4(x^2-2x+2) dẹp luôn
=(x^2-2x+2)(x^2+4)
\(\left(x^2-x+2\right)^2+\left(x-2\right)^2\)
\(=\left[\left(x-2\right)\left(x+1\right)\right]^2+\left(x-2\right)^2\)
\(=\left(x-2\right)^2\left(x+1\right)^2+\left(x-2\right)^2\)
\(=\left(x-2\right)^2\left(x^2+2x+1\right)+\left(x-2\right)^2\)
\(=\left(x-2\right)^2\left(x^2+2x+2\right)\)
\(=a^2b+ab^2-b^2c-bc^2-ac^2+a^2c\)
\(=a^2\left(b+c\right)+a\left(b-c\right)\left(b+c\right)-bc\left(b+c\right)\)
\(=\left(b+c\right)\left(a^2+ab-ac-bc\right)\)
\(=\left(b+c\right)\left[a\left(a+b\right)-c\left(a+b\right)\right]\)
\(=\left(b+c\right)\left(a+b\right)\left(a-c\right)\)
Ta có b + c = (a + b) + (c – a) nên
A = ab(a + b) – bc[(a + b) + (c – a)] – ac(c – a)
= ab(a + b) – bc(a + b) – bc(c – a) – ac(c – a)
= b(a + b)(a – c) – c(c – a)(b + a)
= (a + b)(a – c)(b + c)
Đáp án cần chọn là: B
\(ab\left(b-a\right)-bc\left(b-c\right)-ac\left(c-a\right)\)ư
\(=ab\left(b-a\right)-bc\left[\left(b-a\right)-\left(c-a\right)\right]-ac\left(c-a\right)\)
\(=ab\left(b-a\right)-bc\left(b-a\right)+bc\left(c-a\right)-ac\left(c-a\right)\)
\(=b\left(b-a\right)\left(a-c\right)+c\left(c-a\right)\left(b-a\right)\)
\(=b\left(b-a\right)\left(a-c\right)-c\left(a-c\right)\left(b-a\right)\)
\(=\left(b-c\right)\left(b-a\right)\left(a-c\right)\)
(bình phương mình ghi số 2 đằng sau nhé!)
=ab2-a2b-b2c+bc2-ac2+a2c
=ab(b-a) - c(b2-a2) +c2(b-a)
=ab(b-a) -c(b-a)(b+a)+c(b-a)
=(b-a)( ab-cb-ca+c)
=(b-a)(a(b-c) -c(b-c))
=(b-a)(b-c)(a-c)