Show that the functions in Exercises 19-26 have exactly one zero in the given interval.
19. f(x) = x²+3x+1, [-2,-1]
20. f(x) = x3 + +7, (-00,0) ++7,
21. g(t) = Vi+V1+1-4, (0,00)
22. g(t) 1 1-t +V1+1-3.1, (-1, 1)