The sum and product of two functions [tex] f(x) [/tex] and [tex] g(x) [/tex], i.e. [tex] (f+g)(x) [/tex] and [tex] (f\cdot g)(x) [/tex] respectively, are simply defined as the sum and product of the expressions that define each function.
So, as for exercise 13, we have
[tex] (f\cdot g)(x) = f(x)\cdot g(x) = (2x^3-5x^2)(2x-1) = 4 x^4- 12 x^3 +5 x^2 [/tex]
Similarly, as for exercise 20, we have
[tex] (g + f)(t) = g(t) + f(f) = (2t+5) + (-t^2+5) = -t^2 + 2t + 10 [/tex]
