The quadratic trinomials f(x) and g(x) are such that f′(x)g′(x)≥|f(x)|+|g(x)| for all real x. Prove that the product f(x)g(x) is equal to the square of some trinomial.
Prove that |x|≥x. It may be helpful to compare each of |3|, |−4.3| and |0| with 3, −4.3 and 0 respectively.