Answer:
The value of
.
Step-by-step explanation:
According to the given problem the value of taken functions are,
and 
Then to estimate the value of f(t) at t=1.2, one can consider the equation of tangent line of the graph of f(x) at a point x=a is,

wnere f(x) is differentiable at the point x=a.
From (1) we can get,

In the present problem a=1, and we know value of f(1) and f'(1).
Hence, at a=1.2 and after finding value of f'(1.2) one can easily find,

which will give the best approximation.