Trigonometry : Simplifying Trigonometric Functions

Study concepts, example questions & explanations for Trigonometry

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Example Questions

Example Question #1 : Simplifying Trigonometric Functions

Simplify the following trionometric function:

\displaystyle \frac{4sin^2(60^{\circ})-tan(45^{\circ})}{3sin(45^{\circ})}

Possible Answers:

\displaystyle 1/2

\displaystyle \frac{2\sqrt{2}}{3}

\displaystyle 3/4

\displaystyle 1

\displaystyle \sqrt{2}/2

Correct answer:

\displaystyle \frac{2\sqrt{2}}{3}

Explanation:

To solve the problem, you need to know the following information:

\displaystyle sin(60^{\circ}) = \frac{\sqrt{3}}{2}

\displaystyle tan(45^{\circ})=1

\displaystyle sin(45^{\circ})=\frac{\sqrt{2}}{2}

Replace the trigonometric functions with these values:

\displaystyle \frac{4sin^2(60^{\circ})-tan(45^{\circ})}{3sin(45^{\circ})}

\displaystyle \frac{4(\frac{\sqrt{3}}{2})^2-(1)}{3(\frac{\sqrt{2}}{2})}

\displaystyle \frac{4(\frac{3}{4})-(1)}{(\frac{3\sqrt{2}}{2})}

\displaystyle \frac{2}{(\frac{3\sqrt{2}}{2})}

\displaystyle \frac{4}{3\sqrt{2}} = \frac{4\cdot \sqrt{2}}{3\sqrt{2}\cdot \sqrt{2}} = \frac{4\sqrt{2}}{6} = \frac{2\sqrt{2}}{3}

Example Question #1 : Simplifying Trigonometric Functions

Simplify the following trigonometric function in fraction form:

\displaystyle cos^{2}(45^{\circ})-sin(30^{\circ})

Possible Answers:

\displaystyle 0

\displaystyle 1/3

\displaystyle 1/2

\displaystyle 1

Correct answer:

\displaystyle 0

Explanation:

To determine the value of the expression, you must know the following trigonometric values:

\displaystyle cos(45^{\circ}) = \frac{\sqrt{2}}{2}

\displaystyle sin (30^{\circ})=\frac{1}{2}

Replacing these values, we get:

\displaystyle cos^{2}(45^{\circ})-sin(30^{\circ})

\displaystyle (\frac{\sqrt{2}}{2})^{2}-\frac{1}{2}

\displaystyle \frac{2}{4}-\frac{1}{2}=\frac{1}{2}-\frac{1}{2}=0

Example Question #2 : Simplifying Trigonometric Functions

\displaystyle tan (x)*sin(x) + sec(x)*(cos x)^{2} =

Possible Answers:

\displaystyle tan (x)

\displaystyle sec (x)

\displaystyle (cos x)^{2}

\displaystyle csc (x)

\displaystyle cos (x)* sin (x)

Correct answer:

\displaystyle sec (x)

Explanation:

\displaystyle tan (x)*sin(x) + sec(x)*(cos x)^{2} =

\displaystyle \frac{sin (x)}{cos (x)}* sin(x) + \frac{1}{cos (x)}*(cos x)^{2} =

\displaystyle \frac{(sin x)^{2} + (cos x)^{2}}{cos (x)} = \frac{1}{cos (x)} = sec (x)

Example Question #2 : Simplifying Trigonometric Functions

Simplify the following expression:

\displaystyle A=cos(\frac{3\pi}{2}+x)+sin (\pi+x)+cos(\frac{\pi}{2}+x)+sin(\pi-x)

Possible Answers:

\displaystyle A=0

\displaystyle A=1

\displaystyle A=sin\ x

\displaystyle A=-sin\ x

\displaystyle A=-1

Correct answer:

\displaystyle A=0

Explanation:

We need to use the following identities:

\displaystyle cos(\frac{3\pi}{2}+x)=sin\ x

\displaystyle sin (\pi+x)=-sin\ x

\displaystyle cos(\frac{\pi}{2}+x)=-sin\ x

\displaystyle sin(\pi-x)=sin\ x

Use these to simplify the expression as follows:

\displaystyle A=cos(\frac{3\pi}{2}+x)+sin (\pi+x)+cos(\frac{\pi}{2}+x)+sin(\pi-x)

\displaystyle \Rightarrow A=sin\ x-sin\ x-sin\ x+sin\ x = 0

Example Question #3 : Simplifying Trigonometric Functions

Give the value of \displaystyle A:

\displaystyle A=\frac{2sin(\frac{\pi}{2})+4cos(\frac{\pi}{2})}{4sin(\frac{\pi}{2})-cos(\frac{\pi}{2})}

Possible Answers:

\displaystyle A=1

\displaystyle A=0.5

\displaystyle A=0

\displaystyle A=1.5

\displaystyle A=2

Correct answer:

\displaystyle A=0.5

Explanation:

\displaystyle sin(\frac{\pi}{2})=1

\displaystyle cos(\frac{\pi}{2})=0

Plug these values in:

\displaystyle A=\frac{2sin(\frac{\pi}{2})+4cos(\frac{\pi}{2})}{4sin(\frac{\pi}{2})-cos(\frac{\pi}{2})}=\frac{2\times 1+4\times 0}{4\times 1-0}=\frac{2}{4}=\frac{1}{2}=0.5

 

 

Example Question #4 : Simplifying Trigonometric Functions

If \displaystyle tan\ x = \frac{1}{4}, solve for \displaystyle D:

\displaystyle D=\frac{sin\ x}{sin\ x-cos\ x}+\frac{sin\ x+cos\ x}{cos\ x}

Possible Answers:

\displaystyle D=\frac{11}{12}

\displaystyle D=\frac{1}{12}

\displaystyle D=-\frac{11}{12}

\displaystyle D=\frac{7}{12}

\displaystyle D=\frac{5}{12}

Correct answer:

\displaystyle D=\frac{11}{12}

Explanation:

\displaystyle tan\ x=\frac{1}{4}\Rightarrow \frac{sin\ x}{cos\ x}=\frac{1}{4}\Rightarrow cos\ x=4sin\ x

Substitute \displaystyle cos\ x=4sin \ x into the expression:

\displaystyle D=\frac{sin\ x}{sin\ x-cos\ x}+\frac{sin\ x+cos\ x}{cos\ x}=\frac{sin\ x}{sin\ x-4sin\ x}+\frac{sin\ x+4sin\ x}{4sin\ x}

\displaystyle \Rightarrow D=\frac{sin\ x}{-3sin\ x}+\frac{5sin\ x}{4sin\ x}

\displaystyle \Rightarrow D=-\frac{1}{3}+\frac{5}{4}=\frac{-4+15}{12}=\frac{11}{12}

Example Question #5 : Simplifying Trigonometric Functions

If \displaystyle cot\ x= 3, give the value of \displaystyle D:

\displaystyle D=\frac{cos^2x}{(sin\ x)(cos\ x)}-\frac{sin\ x+cos\ x}{sin\ x}

Possible Answers:

\displaystyle D=1

\displaystyle D=0

\displaystyle D=-2

\displaystyle D=2

\displaystyle D=-1

Correct answer:

\displaystyle D=-1

Explanation:

 \displaystyle cot\ x=3\Rightarrow \frac{cos\ x}{sin\ x}=3\Rightarrow cos\ x= 3sin\ x

Now substitute \displaystyle cos\ x=3sin\ x into the expression:

\displaystyle D=\frac{cos^2x}{(sin\ x)(cos\ x)}-\frac{sin\ x+cos\ x}{sin\ x}=\frac{(3sin\ x)^2}{(sin\ x)(3sin\ x)}-\frac{sin\ x+3sin\ x}{sin\ x}

\displaystyle \Rightarrow D=\frac{9sin^2x}{3sin^2x}-\frac{4sin\ x}{sin\ x}

\displaystyle \Rightarrow D=\frac{9}{3}-4=3-4=-1

 

Example Question #6 : Simplifying Trigonometric Functions

Simplify the following expression:

\displaystyle A=\frac{sin^2x}{1+tan^2x}-\frac{cos^2x}{1+cot^2x}+1

Possible Answers:

\displaystyle A=-1

\displaystyle A=0

\displaystyle A=2

\displaystyle A=1

\displaystyle A=-2

Correct answer:

\displaystyle A=1

Explanation:

We need to use the following identitities:

\displaystyle \frac{1}{cos ^2x}=1+tan^2x

\displaystyle \frac{1}{sin^2x}=1+cot^2x

Now substitute them into the expression:

\displaystyle A=\frac{sin^2x}{1+tan^2x}-\frac{cos^2x}{1+cot^2x}+1=\frac{sin^2x}{\frac{1}{cos^2x}}-\frac{cos^2x}{\frac{1}{sin^2x}}+1

\displaystyle \Rightarrow A=(sin^2x)(cos^2x)-(sin^2x)(cos^2x)+1=0+1=1

Example Question #1 : Simplifying Trigonometric Functions

If  \displaystyle cos\ x=\frac{1}{3} and \displaystyle sin\ x\neq 0, give the value of \displaystyle \frac{sin\ x+sin\ 2x}{sin\ x-sin\ 2x}.

Possible Answers:

\displaystyle 4

\displaystyle 5

\displaystyle 1

\displaystyle 2

\displaystyle 3

Correct answer:

\displaystyle 5

Explanation:

Based on the double angle formula we have, \displaystyle sin\ 2x=2(sin\ x)(cos\ x).

\displaystyle \frac{sin\ x+sin\ 2x}{sin\ x-sin\ 2x}=\frac{sin\ x+2(sin\ x)(cos\ x)}{sin\ x-2(sin\ x)(cos\ x)}

\displaystyle =\frac{sinx(1+2cos\ x )}{sinx(1-2cos\ x )}=\frac{1+2cos\ x}{1-2cos\ x}

\displaystyle =\frac{1+2(\frac{1}{3})}{1-2(\frac{1}{3})}=\frac{\frac{3+2}{3}}{\frac{3-2}{3}}=5

 

Example Question #2 : Simplifying Trigonometric Functions

If \displaystyle x=\frac{\pi}{3}, give the value of \displaystyle \frac{sin\ x}{sin\ x+cos\ 2x}.

Possible Answers:

\displaystyle \frac{3+\sqrt{3}}{2}

\displaystyle \frac{3-\sqrt{3}}{2}

\displaystyle 3

\displaystyle \frac{3+\sqrt{2}}{2}

\displaystyle \frac{3-\sqrt{2}}{2}

Correct answer:

\displaystyle \frac{3+\sqrt{3}}{2}

Explanation:

\displaystyle x=\frac{\pi}{3}\Rightarrow sin\ x=sin(\frac{\pi}{3})=\frac{\sqrt{3}}{2}

Now we can write:

\displaystyle x=\frac{\pi}{3}\Rightarrow 2x=2(\frac{\pi}{3})=\frac{2\pi}{3}\Rightarrow cos\ 2x=cos(\frac{2\pi}{3})

\displaystyle =cos(\pi-\frac{\pi}{3})

\displaystyle =-cos (\frac{\pi}{3})

\displaystyle =-\frac{1}{2}

Now we can substitute the values:

\displaystyle \frac{sin\ x}{sin\ x+cos\ 2x}=\frac{\frac{\sqrt{3}}{2}}{\frac{\sqrt{3}}{2}-\frac{1}{2}}=\frac{\sqrt{3}}{\sqrt{3}-1}=\frac{\sqrt{3}}{\sqrt{3}-1}\times \frac{{\sqrt{3}+1}}{{\sqrt{3}+1}}=\frac{3+\sqrt{3}}{2}

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