Question

how to factor 5x^2 +4x -1

Answer 1

$5x^2+4x-1\\\\Method\ 1:\\\\5x^2+4x-1=5x^2+5x-x-1=5x(x+1)-1(x+1)\\=(x+1)(5x-1)\\\\5x^2+4x-1=(x+1)(5x-1)\\\\Method\ 2:\\\\5x^2+4x-1\\a=5;\ b=4;\ c=-1\\\\\Delta=b^2-4ac\\\\\Delta=4^2-4\cdot5\cdot(-1)=16+20=36 \ \textgreater \ 0\\\\x_1=\dfrac{-b-\sqrt\Delta}{2a}\ and\ x_2=\dfrac{-b+\sqrt\Delta}{2a}\\\\\sqrt\Delta=\sqrt{36}=6\\\\x_1=\dfrac{-4-6}{2\cdot5}=\dfrac{-10}{10}=-1\\\\x_2=\dfrac{-4+6}{2\cdot5}=\dfrac{2}{10}=0.2\\\\5x^2+4x-1=5(x-0.2)(x+1)=(5x-1)(x+1)$