SAT II Math I : Secant, Cosecant, Cotangent

Study concepts, example questions & explanations for SAT II Math I

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Example Questions

Example Question #1 : Secant, Cosecant, Cotangent

If \displaystyle \cot \alpha = 5 and \displaystyle \sin \alpha < 0, what is the value of \displaystyle \sec \alpha?

Possible Answers:

\displaystyle \sqrt{26}

\displaystyle -\frac{5}{\sqrt{26}}

\displaystyle -\frac{\sqrt{26}}{5}

\displaystyle \frac{\sqrt{26}}{5}

\displaystyle -\frac{1}{\sqrt{26}}

Correct answer:

\displaystyle -\frac{\sqrt{26}}{5}

Explanation:

Since cotangent is positive and sine is negative, alpha must be in quadrant III.  \displaystyle \cot \alpha = \frac{x}{y} then implies that \displaystyle (x,y)=(-5,-1) is a point on the terminal side of alpha. 

\displaystyle r=\sqrt{(x^2+y^2)}=\sqrt{26}

\displaystyle \sec \alpha = \frac{r}{x} = \frac{\sqrt{26}}{-5}

Example Question #2 : Secant, Cosecant, Cotangent

If \displaystyle \csc \theta < 0 and \displaystyle \tan \theta > 0, then which of the following must be true about \displaystyle \theta.

Possible Answers:

\displaystyle \frac{\pi}{2} < \theta < \pi

\displaystyle 0 < \theta < \frac{\pi}{2}

\displaystyle \pi < \theta < \frac{3\pi}{2}

\displaystyle \frac{3\pi}{2} < \theta < 2\pi

\displaystyle -\frac{\pi}{2} < \theta < 0

Correct answer:

\displaystyle \pi < \theta < \frac{3\pi}{2}

Explanation:

Since cosecant is negative, theta must be in quadrant III or IV. 

Since tangent is positive, it must be in quadrant I or III. 

Therefore, theta must be in quadrant III.

Using a unit circle we can see that quadrant III is when theta is between \displaystyle \pi and \displaystyle \frac{3\pi}{2}.

Example Question #2 : Secant, Cosecant, Cotangent

The point \displaystyle (12, 5) lies on the terminal side of an angle in standard position. Find the secant of the angle.

Possible Answers:

\displaystyle \frac{5}{13}

\displaystyle \frac{5}{12}

\displaystyle \frac{13}{5}

\displaystyle \frac{12}{13}

\displaystyle \frac{13}{12}

Correct answer:

\displaystyle \frac{13}{12}

Explanation:

Secant is defined to be the ratio of \displaystyle r to \displaystyle x where \displaystyle r is the distance from the origin. 

The Pythagoreanr Triple 5, 12, 13 helps us realize that \displaystyle r = 13

Since \displaystyle x = 12, the answer is \displaystyle \frac{13}{12}.

Example Question #3 : Secant, Cosecant, Cotangent

Given angles \displaystyle x and \displaystyle y in quadrant I, and given,

 \displaystyle \sin x = \frac{3}{5} and \displaystyle \cos y = \frac {5}{13},

find the value of \displaystyle \csc (x+y).

Possible Answers:

\displaystyle \frac {65}{63}

\displaystyle \frac {65}{64}

\displaystyle \frac {99}{65}

\displaystyle \frac {63}{65}

\displaystyle \frac {65}{64}

Correct answer:

\displaystyle \frac {65}{63}

Explanation:

Use the following trigonometric identity to solve this problem.

\displaystyle \csc (x+y) = \frac {1}{\sin (x+y)} = \frac {1}{\sin x \cos y + \cos x \sin y}

Using the Pythagorean triple 3,4,5, it is easy to find \displaystyle \cos x = \frac {4}{5}.

Using the Pythagorean triple 5,12,13, it is easy to find \displaystyle \sin y = \frac {12}{13}.

So substituting all four values into the top equation, we get

\displaystyle \csc (x+y) = \frac {1}{\frac {3}{5} \cdot \frac {5}{13} + \frac {4}{5} \cdot \frac {12}{13}} = \frac {65}{63}

Example Question #4 : Secant, Cosecant, Cotangent

Find the value of the trigonometric function in fraction form for triangle \displaystyle ABC.

Triangle

What is the secant of \displaystyle \angle A?

Possible Answers:

\displaystyle 7/25

\displaystyle \frac{25}{24}

\displaystyle 24/25

\displaystyle 24/7

\displaystyle 25/7

Correct answer:

\displaystyle \frac{25}{24}

Explanation:

The value of the secant of an angle is the value of the hypotenuse over the adjacent.

Therefore:

\displaystyle sec \angle A = \frac{hypotenuse}{adjacent} = \frac{25}{24}

Example Question #5 : Secant, Cosecant, Cotangent

Which of the following is the equivalent to \displaystyle \frac{1}{\csc\theta}?

Possible Answers:

\displaystyle \cot\theta

\displaystyle \sec\theta

\displaystyle \tan\theta\sin\theta

\displaystyle \cos\theta

\displaystyle \sin\theta

Correct answer:

\displaystyle \sin\theta

Explanation:

Since \displaystyle \csc\theta=\frac{1}{\sin\theta}:

 \displaystyle \frac{1}{\csc\theta}=\frac{1}{\frac{1}{\sin\theta}}=1*\frac{\sin\theta}{1}=\sin\theta

Example Question #6 : Secant, Cosecant, Cotangent

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For the above triangle, what is \displaystyle \sec (\theta) if \displaystyle o = 8\displaystyle a = 15 and \displaystyle h = 17?

Possible Answers:

\displaystyle 0.53

\displaystyle 0.88

\displaystyle {}1.13

\displaystyle 0.47

\displaystyle 2.13

Correct answer:

\displaystyle {}1.13

Explanation:

Secant is the reciprocal of cosine.

\displaystyle \sec \left ( \theta\right ) = \frac{1}{\cos \left ( \theta\right )}

It's formula is:

Substituting the values from the problem we get,

\displaystyle \sec(\theta) = \frac{17}{15} = 1.13

 

 

Example Question #7 : Secant, Cosecant, Cotangent

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For the above triangle, what is \displaystyle \cot (\theta) if \displaystyle o = 18\displaystyle a = 24 and \displaystyle h = 30?

Possible Answers:

\displaystyle 1.67

\displaystyle 1.33

\displaystyle 0.60

\displaystyle 1.25

\displaystyle 0.75

Correct answer:

\displaystyle 1.33

Explanation:

Cotangent is the reciprocal of tangent.

\displaystyle \cot \left ( \theta\right ) = \frac{1}{\tan \left ( \theta\right )}

It's formula is:

Substituting the values from the problem we get,

\displaystyle \cot(\theta) = \frac{24}{18} = 1.33

 

Example Question #2 : Sec, Csc, Ctan

Determine the value of \displaystyle cot(\frac{\pi}{4}).

Possible Answers:

\displaystyle 1

\displaystyle \frac{\sqrt2}{2}

\displaystyle \frac{1}{2}

\displaystyle \infty

\displaystyle 0

Correct answer:

\displaystyle 1

Explanation:

Rewrite \displaystyle cot(\frac{\pi}{4}) in terms of sine and cosine.

\displaystyle cot(\frac{\pi}{4})= \frac{cos(\frac{\pi}{4})}{sin(\frac{\pi}{4})}=\frac{\frac{\sqrt2}{2}}{\frac{\sqrt2}{2}}=1

Example Question #4 : Secant, Cosecant, Cotangent

Evaluate:  \displaystyle sec(60)-csc(45)

Possible Answers:

\displaystyle 2+\sqrt2

\displaystyle 2+\frac{\sqrt2}{2}

\displaystyle 2\sqrt2+2

\displaystyle 2-\sqrt2

\displaystyle 2-\frac{\sqrt2}{2}

Correct answer:

\displaystyle 2-\sqrt2

Explanation:

Evaluate each term separately.

\displaystyle sec(60)= \frac{1}{cos(60)}=\frac{1}{0.5}= 2

\displaystyle csc(45)= \frac{1}{sin(45)}= \frac{1}{\frac{\sqrt2}{2}}= \frac{2}{\sqrt2}\times\frac{\sqrt2}{\sqrt2}= \frac{2\sqrt2}{2}=\sqrt2

\displaystyle sec(60)-csc(45)=2-\frac{2\sqrt2}{2}=2-\sqrt2

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