Answer:

Step-by-step explanation:
Given


![Interval: [1,8]](https://tex.z-dn.net/?f=Interval%3A%20%5B1%2C8%5D)

Required
Find c using Intermediate Value theorem
First, check if the value of M is within the given range:







M is within range.
Solving further:
We have:


Substitute 21 for f(x) in 

Express as quadratic function


Expand



or 
or 
The value of
is outside the ![Interval: [1,8]](https://tex.z-dn.net/?f=Interval%3A%20%5B1%2C8%5D)
So:



By comparison:

the answer is no. the solution is (1.333, 7.333)
The height of a dam:
h = x + 1.65 m,
where:
x = 90 m · tan 26°
x = 90 · 0.4877
x = 43.90
h = 43.90 m + 1.65 m = 45.55 m
Answer:
The height of the dam is 45.5 m.