a ) Sai đề : \(21bc^2+6c+3c^3+42b\)
\(=3c^2\left(7b+c\right)+6\left(7b+c\right)\)
\(=\left(3c^2+6\right)\left(7b+c\right)\)
\(=3\left(c^2+2\right)\left(7b+c\right)\)
b ) \(a^2+b^2+2a-2b-2ab\)
\(=\left(a^2-2ab+b^2\right)+2\left(a-b\right)\)
\(=\left(a-b\right)\left(a-b+2\right)\)
c ) \(x^2-5x+4\)
\(=x^2-4x-x+4\)
\(=x\left(x-4\right)-\left(x-4\right)\)
\(=\left(x-1\right)\left(x-4\right)\)
a)Sai đề nha bạn
\(21bc^2+6c+3c^3+42b=3c^2\left(7b+3c\right)+6\left(7b+c\right)=\left(3c^2+6\right)\left(7b+c\right)\)
b)\(a^2+b^2+2a-2b-2ab=a^2-2ab+b^2+2a-2b=\left(a-b\right)^2+2\left(a-b\right)=\left(a-b\right)\left(a-b+2\right)\)
c)\(x^2-5x+4=x^2-x-4x+4=x\left(x-1\right)-4\left(x-1\right)=\left(x-4\right)\left(x-1\right)\)
