Answer:

Step-by-step explanation:
Given that:

We are given the 2nd derivative of a function f(x) and we need to find f(x) from that.
We will have to integrate it twice to find the value of f(x).
Let us have a look at the basic formula of integration that we will use in the solution:


Now, integrating it again to find f(x):

We know that
sin²x+cos²x=1
so
clear cos x
cos x=(+/-)√[1-sin²x]
in this problem
<span>Angle 0 is in quadrant 1 -----> cos o and sin o are positive
</span>sin o=2/5
cos x=√[1-(2/5)²]----> cos o=√[1-4/25]----> cos o=√[21/25]---> cos o=√21/5
the answer is
cos o=√21/5