What are the zeros of f left parenthesis x right parenthesis equals x cubed minus 57 x plus 56 ?

F (x) = x^3-57x+56

Regroup to factor it: f (x) = x^3-x-56x-56 = (x^3-x) - (56x+56)

f (x) = x (x^2-1) - 56 (x+1)

f (x) = x (x+1) (x-1) - 56 (x+1)

f (x) = (x-1) [x (x+1) - 56] = (x-1) (x^2+x-56) = (x-1) (x+8) (x-7)

the zeros are the values of x when f (x) = o

(x-1) (x+8) (x-7) = 0

x=1, - 8, 7