Math Olympiad | A Nice Algebra Math Problem | Find the Value of x 

by faktoring , x^4-6x^3-5x^2+42x+40=0 , -> (x-4)(x^3-2x^2-13x-10)=0 , x-4=0 , x=4 , x^3-2x^2-13x-10=0 , -> (x+2)(x^2-4x-5)=0 , x+2=0 , x=-2 , x^2-4x-5=0 , (x-5)(x+1)=0 , x-5=0 , x=5 , x+1=0 , x= - 1 , Solu. , x= 4 , - 2 ,5 , - 1 ,