i have to solve this how I got y(3)+5y(2)-4y-20?

Answer 1

what does y(3) and y(2) mean? Do you mean exponent, as in

y^3+5y^3-4y-20=0 ? That is easy, factor out the common factor:

y^2*( y+5)-4(y+5)=0 and shazam you have
(y^2-4)(y+5)=0
(y+2)(y-2)(y+5)=0
so y= +-2, or -5