Answer:
a = 8
b = -8
Step-by-step explanation:
You have the following function:
[tex]f(x)\\\\=at+b;\ \ t<2\\\\2t^2-1;\ \ 2\leq t[/tex]
A function is differentiable at a point c, if the derivative of the function in such a point exists. That is, f'(c) exists.
In this case, you need that the function is differentiable for t=2, then, you have:
[tex]f'(t)=a;\ \ \ \ t<2 \\\\f'(t)=4t;\ \ \ 2\leq t[/tex]
If the derivative exists for t=2, it is necessary that the previous derivatives are equal:
[tex]f'(2)=a=4(2)\\\\a=8[/tex]
Furthermore it is necessary that for t=2, both parts of the function are equal:
[tex]8(2)+b=2(2)^2-1\\\\16+b=8-1\\\\b=-8[/tex]
Then, a = 8, b = -8
