a) \(\Leftrightarrow\left(x+4\right)^2=100\Rightarrow x+4=+-10\Leftrightarrow x=-4+-10\)( bước kia được ^2 là nhân chéo nha)

b) \(\left(x-1\right)\left(x+3\right)=\left(x+2\right)\left(x-2\right)\Leftrightarrow x^2+2x-3=x^2-4\Leftrightarrow2x=-1\Leftrightarrow x=-\frac{1}{2}\)

\(D=a^3\left(b-c\right)+b^3\left(c-a\right)+c^3\left(a-b\right)\)

\(D=a^3\left(b-c\right)+\left[b^3\left(c-a\right)+c^3\left(a-b\right)\right]\)

\(D=a^3\left(b-c\right)\left(b^3c-ab^3+ac^3-bc^3\right)\)

\(D=a^3\left(b-c\right)\left[\left(b^3c-bc^3\right)-\left(ab^3-ac^3\right)\right]\)

\(D=a^3\left(b-c\right)\left[bc\left(b^2-c^2\right)-a\left(b^3-c^3\right)\right]\)

\(D=a^3\left(b-c\right)\left[bc\left(b-c\right)\left(b+c\right)-a\left(b-c\right)\left(b^2+bc+c^2\right)\right]\)

\(D=\left(b-c\right)\left[a^3+bc\left(b+c\right)-a\left(b^2+bc+c^2\right)\right]\)

\(D=\left(b-c\right)\left(a^3+b^2c+bc^2-ab^2-abc-ac^2\right)\)

\(D=\left(b-c\right)\left[\left(b^2c-ab^2\right)+\left(bc^2-abc\right)-\left(ac^2-a^3\right)\right]\)

\(D=\left(b-c\right)\left[b^2\left(c-a\right)+bc\left(c-a\right)-a\left(c^2-a^2\right)\right]\)

\(D=\left(b-c\right)\left[b^2\left(c-a\right)+bc\left(c-a\right)-a\left(c-a\right)\left(c+a\right)\right]\)

\(D=\left(b-c\right)\left(c-a\right)\left[b^2+bc-a\left(c+a\right)\right]\)

\(D=\left(b-c\right)\left(c-a\right)\left(b^2+bc-ac-a^2\right)\)

\(D=\left(b-c\right)\left(c-a\right)\left[\left(bc-ac\right)+\left(b^2-a^2\right)\right]\)

\(D=\left(b-c\right)\left(c-a\right)\left[c\left(b-a\right)+\left(b-a\right)\left(b+a\right)\right]\)

\(D=\left(b-c\right)\left(c-a\right)\left(b-a\right)\left(c+b+a\right)\)

\(D=\left(a-b\right)\left(b-c\right)\left(a-c\right)\left(a+b+c\right)\)

Chúc bạn học tốt.

cái này có trong đề thi lớp 8 của Đô Lương (2017-2018) nè

Không Biết Tên có phải bạn ở Nghệ An không ?

a. (a-b)^2 = (a-b)(a-b) = a^2 - ab - ba + b^2 = a^2 - 2ab + b^2

b. (a+b)^3= (a+b)(a+b)(a+b) = (a^2 + 2ab + b^2)(a + b) = a^3 + a^2b + 2a^2b + 2ab^2 + ab^2 + b^3 = a^3 + 3a^2b + 3b^2a + b^3

c. (a-b)^3= (a - b)(a-b)(a-b) = (a^2 - 2ab + b^2)(a - b) = a^3 - a^2b - 2a^2b + 2ab^2 + b^2a - b^3 = a^3 - 3a^2b + 3ab^2 - b^3

e. (a-b) ( a^2 + ab +b^2) = a^3 + a^2b + b^2a - ba^2 - ab^2 - b^3 = a^3 - b^3

g. ( a-b) ( a+b) = a^2 +ab -ab - b^2 = a^2 - b^2