Answer:

Explanation:
We want to write the trignometric expression:

As an algebraic equation.
First, we can focus on the inner expression. Let θ equal the expression:

Take the secant of both sides:

Since secant is the ratio of the hypotenuse side to the adjacent side, this means that the opposite side is:

By substitutition:

Using an double-angle identity:

We know that the opposite side is √(u² -100), the adjacent side is 10, and the hypotenuse is u. Therefore:

Simplify. Therefore:
