Question 30237
Solve for y: 
y^4-4y^2=40y-10y^3  ----(1)
(taking all the terms to the left side changin sign while changing side)
y^4+10y^3-4y^2-40y=0
y[y^3+10y^2-4y-40]=0
y[y^2(y+10)-4(y+10)] = 0
y[y^2p-4p] = 0 where p =(y+10)
yp(y^2-4)=0
y(y+10)(y+2)(y-2) = 0
Therefore y =0,(y+10) = 0, (y+2) = 0, (y-2) = 0
That is y = 0, y =-10, y =-2, y = 2

Which is your choice  (c) 0, -10, 2, -2