Select the number line that represents all solutions of x 13.5

3rd.

Step-by-step explanation:

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A.)

   

Use the identities  and  on the left-hand side

   

Make 1 have a common denominator to allow for fraction subtraction
Multiply the numerator and denominator of 1 by cos^2 x

   

Use Pythagorean identity for the numerator.

If  then subtracting both sides by  yields . We can substitute that into the numerator

   

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b.)

   

For the left-hand side:
By definition,  and 

   

Since 

   

Using Pythagorean identity,  so