\(1.3x^2-x-10=3x^2+5x-6x-10=x\left(3x+5\right)-2\left(3x+5\right)=\left(3x+5\right)\left(x-2\right)\) \(2.2x^2+3x-9=2x^2-3x+6x-9=x\left(2x-3\right)+3\left(2x-3\right)=\left(2x-3\right)\left(x+3\right)\) \(3.2x^4-5x-7=2x^4+2x-7x-7=2x\left(x^3+1\right)-7\left(x+1\right)=2x\left(x+1\right)\left(x^2-x+1\right)-7\left(x+1\right)=\left(x+1\right)\left(2x^3-2x^2+2x-7\right)\)
a)
\(3x^2-x-10\)
\(\Leftrightarrow3x^2-6x+5-10\)
\(\Leftrightarrow3x\left(x-2\right)+5\left(x-2\right)\)
\(\Leftrightarrow\left(x-2\right)\left(3x+5\right)\)
b) Đề sai nha bạn, mình mạo phép sửa lại tí nghen!
\(2x^2+3x-9\)
<=>\(2x^2-3x+6x-9\)
\(\Leftrightarrow2x\left(x+3\right)-3\left(x+3\right)\)
\(\Leftrightarrow\left(x+3\right)\left(2x-3\right)\)
c)
\(2x^4-5x-7\)
\(\Leftrightarrow2x^4-2x^3-2x^2-7x+2x^3+2x^2+2x-7\)
\(\Leftrightarrow2x^4-5x-7x-7\)
\(\Leftrightarrow\left(x+1\right)\left(2x^3-2x^2+2x-7\right)\)
Chúc bạn học tốt! ^^