78 . Hope this was helpful
Answer: 
Step-by-step explanation:
Observe in the figure given in the exercise that four right triangles are formed.
In this case you can use the following Trigonometric Identity to solve this exercise:
From the figure you can identify that:

Then, you can substitute values:

The next step is to solve for DE in order to find its value. This is:

Finally, rounding the result to the nearest tenth, you get that this is:

Answer:
(a) If r is any rational number and s is any irrational number, then r/s is rational
(b) The statement is false when r is 0
Step-by-step explanation:
Given
rational number
irrational number
irrational number
Solving (a): The negation
To get the negation of a statement, we only need to negate the end result
In other words, the number type of r and s will remain the same, but r/s will be negated.
So, the negation is:
rational number
irrational number
rational number
Solving (b): When r/s is irrational is false
Given that:
irrational number
Set r to 0
So:

-- rational
<em>Hence, the statement is false when r is 0</em>