a. 13-16 Use the definition of continuity and the properties of limits to show that the function is continuous at the given number 13. f(x)=3x+(x+2), a = -1 t + 5t 14. g(t) = a = 2 2t+1' 15. p(v) = 2/3v + 1, a = 1 16. f(r) = 4r22r+7, a = -2 17-18 Use the definition of continuity and the properties of limits to show that the function is continuous on the given interval. 17. f(x) = x + x-4, [4,) x-1 18. g(x) = (-0,-2) 3x+6