The expression that is not a variation of the Pythagorean identity is the third option.
<h3>
What is the Pythagorean identity?</h3>
The Pythagorean identity can be written as:

For example, if we subtract cos^2(x) on both sides we get the second option:

Which is a variation.
Now, let's divide both sides by cos^2(x).

Notice that the third expression in the options looks like this one, but the one on the right side is positive. The above expression is in did a variation of the Pythagorean identity, then the one written in the options (with the 1 instead of the -1) is incorrect, meaning that it is not a variation of the Pythagorean identity.
Concluding, the correct option is the third one.
If you want to learn more about the Pythagorean identity, you can read:
brainly.com/question/24287773
20,000÷50=

The plane needs to descend at 400 ft per mile.
At 40 degrees?
Answer:
10 in
Step-by-step explanation:
There are two ways to work this problem, and they give different answers. The reason for that is that <em>the data shown in the diagram is not consistent</em>.
<u>Method 1</u>
Use the area to determine the base length. The area formula is ...
A = (1/2)bh
20 in^2 = (1/2)(b)(4 in)
(20 in^2)/(2 in) = b = 10 in
The missing side dimension is 10 inches.
__
<u>Method 2</u>
Use the Pythagorean theorem to find the parts of the base, then add them up.
Left of the "?" we have ...
left^2 +4^ = 6^
left^2 = 36 -16 = 20
left = √20 = 2√5
Right of the "?" we have ...
right^2 +4^2 = 8^2
right^2 = 64 -16 = 48
right = √48 = 4√3
So, the base length is ...
base = left + right = 2√5 +4√3
base ≈ 11.400 in
The missing side dimension is 11.4 inches. (The area is 22.8 in^2.)
You can complete this by solving:

Which should give you .274418 or 27.44%
2 is the base number beside 3/5