Find the squareroot and standard form of the polynomial func

Find the squareroot and standard form of the polynomial function with the given squareroots and y-intercept. squareroots: {-1,-1,1, 2};f(0) = -20

here roots are (-1,-1,1,2)&f(0)=-20

to find factors we subtract roots so we get x+1,x+1,x-1,x-2.

therefore the general from of polnomial is

f(X)=a(x+1)(x+1)(x-1)(x-2)

f(0)=a(0+1)(0+1)(0-1)(0-2)

-20=2a

a=-10

f(x)=-10(x+1)(x+1)(x-1)(x-2)

=-10(x+1)(x^2-1)(x-2)

=-10(x^4-x^3-3x^2+x+2)

=-10x^4+10x^3+3x^2-10x-20

clearly it roots are -1,-1,1,2 because we make polynomial using these roots.