Question

giúp e bài 2, 3, 4 với mn ko bỏ bước ạ 

Answer 1

Bài 2: 

a:\(18a^2b-54a^2b^2+72ab\)

\(=18ab\left(a-3ab+4\right)\)

b: \(7a-b^2+7b-ab\)

\(=7\left(a+b\right)-b\left(a+b\right)\)

\(=\left(a+b\right)\left(7-b\right)\)

c: \(a^2-9b^2-6a+9\)

\(=\left(a-3\right)^2-9b^2\)

\(=\left(a-3-3b\right)\left(a-3+3b\right)\)

Bài 4: 

Ta có: \(X=a^3-3a^2+3a\)

\(=a^3-3a^2+3a-1+1\)

\(=\left(a-1\right)^3+1\)

\(=100^3+1=1000001\)

Answer 2

Bài 3: 

a: Ta có: \(5a\left(5a-1\right)-\left(5a+1\right)\left(5a-1\right)=8\)

\(\Leftrightarrow25a^2-5a-25a^2+1=8\)

\(\Leftrightarrow5a=-7\)

hay \(a=-\dfrac{7}{5}\)

b: Ta có: \(a^2-3a+9-3a=0\)

\(\Leftrightarrow a\left(a-3\right)-3\left(a-3\right)=0\)

\(\Leftrightarrow\left(a-3\right)^2=0\)

\(\Leftrightarrow a-3=0\)

hay a=3