Answer:

Step-by-step explanation:
Given

Required
Solve
Let

Differentiate



Make dx the subject

The given integral becomes:



Recall that: 
Make
the subject

Square both sides


Substitute
for
in 

Simplify



In standard integration

So, the expression becomes:


Recall that: 

Answer:

Step-by-step explanation:

State that the values where cos x is minimum:






77/5=99/x
77x=5*99
77x=495
x=495/77
x=6.4
she needs to study 6.4 hrs to get 99