High School Math : Trigonometry

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : Trigonometric Identities

Simplify:

\(\displaystyle \sin^2x+\cos^2x+\tan^2x\)

Possible Answers:

\(\displaystyle \csc^2 x\)

\(\displaystyle \sin x\cos x\)

\(\displaystyle \sec^2x\)

\(\displaystyle 2\cos x+\cot x\)

This is the most simplified version.

Correct answer:

\(\displaystyle \sec^2x\)

Explanation:

Whenever you see a trigonometric function squared, start looking for a Pythagorean identity.

The two identities used in this problem are \(\displaystyle \sin^2 x + \cos ^2 x=1\) and \(\displaystyle \tan^2 x +1 =\sec^2 x\).

Substitute and solve.

\(\displaystyle \sin^2x+\cos^2x+\tan^2x=?\)

\(\displaystyle (\sin^2x+\cos^2x)+\tan^2x=?\)

\(\displaystyle (1)+\tan^2x=\sec^2 x\)

Example Question #1 : Using Identities Of Squared Functions

Factor and simplify \(\displaystyle \frac{\sin^2x-9}{\sin x-3}\).

Possible Answers:

\(\displaystyle \sin x \cos x\)

\(\displaystyle \sin x+3\)

\(\displaystyle \cos^2 x+3\)

\(\displaystyle \csc x\)

This is already it's most reduced form.

Correct answer:

\(\displaystyle \sin x+3\)

Explanation:

To reduce \(\displaystyle \frac{\sin^2x-9}{\sin x-3}\), factor the numerator: \(\displaystyle \frac{(\sin x-3)(\sin x+3)}{\sin x-3}\)

Notice that we can cancel out a \(\displaystyle \sin x -3\).

This leaves us with \(\displaystyle \sin x +3\).

Example Question #1 : Using Sum And Product Identities

Simplify \(\displaystyle \sin x\cot x\).

Possible Answers:

\(\displaystyle \sin x \cos x\)

\(\displaystyle cos \, x\)

\(\displaystyle \cos^2x\)

\(\displaystyle \csc x\)

\(\displaystyle \tan x\)

Correct answer:

\(\displaystyle cos \, x\)

Explanation:

To simplify \(\displaystyle \sin x\cot x\), break them into their SOHCAHTOA parts:

\(\displaystyle \frac{\text{opposite}}{\text{hypotenuse}}*\frac{\text{adjacent}}{\text{opposite}}\).

Notice that the opposite's cancel out, leaving \(\displaystyle \frac{\text{adjacent}}{\text{hypotenuse}}=\cos x\).

Example Question #1 : Using Sum And Product Identities

Simplify \(\displaystyle \csc x \tan x\).

Possible Answers:

\(\displaystyle \sec x\)

\(\displaystyle \cos x\)

This is the most simplified version.

\(\displaystyle 1\)

\(\displaystyle \sin x \cos x\)

Correct answer:

\(\displaystyle \sec x\)

Explanation:

Break down \(\displaystyle \csc x \tan x\) into SOHCAHTOA to solve:

\(\displaystyle \csc=\frac{\text{hypotenuse}}{\text{opposite}}\) and \(\displaystyle \tan=\frac{\text{opposite}}{\text{adjacent}}\).

Therefore, \(\displaystyle \csc x \tan x=\frac{\text{hypotenuse}}{\text{opposite}}*\frac{\text{opposite}}{\text{adjacent}}\). Note that the opposite's cancel out, leaving \(\displaystyle \frac{\text{hypotenuse}}{\text{adjacent}}\), which is the same as \(\displaystyle \sec x\).

Example Question #1 : Using Identities Of Inverse Operations

\(\displaystyle \textup{Which of the following expressions is equal to }\frac{\tan \theta }{\sec \theta }\:\textup{?}\)

Possible Answers:

\(\displaystyle \sin\theta\)

\(\displaystyle \cot\theta\)

\(\displaystyle \csc\theta\)

\(\displaystyle \cos\theta\)

\(\displaystyle \frac{1}{\cos ^{2}\theta }\)

Correct answer:

\(\displaystyle \sin\theta\)

Explanation:

\(\displaystyle \textup{Use identities to solve: }\tan\theta=\frac{\sin \theta }{\cos \theta }\:\:\:\:\:\sec\theta=\frac{1}{\cos \theta }\)

\(\displaystyle \frac{\tan \theta }{\sec \theta }=\frac{\sin \theta }{\cos \theta }\times\frac{\cos \theta }{1}=\sin\theta\)

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