Right Triangle Trigonometry – Part 2

Last week I began going over the fundamentals of right triangle trigonometry. I suggest that you review the material in that post before continuing on with this one. You can find that post here: Right Triangle Trigonometry – Part 1

Let’s quickly review the six basic trigonometric functions: 

Very often in trigonometry problems on standardized tests the Pythagorean Theorem is needed to get the final answer.

The Pythagorean Theorem: If a right triangle has legs of length a and b, and a hypotenuse of length c, then c² = a² + b².

Example 3

Notes: (1) The most common Pythagorean triples are 3,4,5 and 5, 12, 13. Two others that may come up are 8, 15, 17 and 7, 24, 25.

(2) If you don’t remember the Pythagorean triple 5, 12, 13, you can use the Pythagorean Theorem:

Here we have 5² + b² = 13². Therefore 25 + b² = 169. Subtracting 25 from each side of this equation gives b² = 169 – 25 = 144. So b = 12.

(3) The equation b² = 144 would normally have solutions b = 12 and b = –12. But the length of a side of a triangle cannot be negative, so we reject –12.

More Trigonometry Practice Problems

If you are preparing for the ACT, SAT or an SAT math subject test, you may want to take a look at one of the books from the Get 800 collection of test prep books.

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