Answer :
a) f(x) = 0 <=> x = -1 or x = 2 or x = 3;
b) x∈(-oo, -1) => f(x) < 0;
x∈(-1, 2) => f(x) > 0;
x∈(2, 3) => f(x) < 0;
x∈(3, +oo) => f(x) > 0;
b) x∈(-oo, -1) => f(x) < 0;
x∈(-1, 2) => f(x) > 0;
x∈(2, 3) => f(x) < 0;
x∈(3, +oo) => f(x) > 0;