Step-by-step explanation:
[tex]19.\\2x^2=(2)\bold{(x)}(x)\\x=(1)\bold{(x)}\\2x^2+x=\bold{x}(2x+1)\\\\20.\\12x^5=\bold{(3)(4)(x)}(x)(x)(x)(x)\\36x=\bold{(3)(4)}(3)\bold{(x)}\\12x^5-36x=\bold{(3)(4)(x)}(x^4-3)=\bold{12x}(x^2-3)\\\\21.\\15x=(3)\bold{(5)}(x)\\5y^2=\bold{(5)}(y)(y)\\15x-5y^2=\bold{5}(3x-y^2)[/tex]
