ACT Math : How to find positive cosine

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find Positive Cosine

The value of a cosine is positive in which quadrants?

 

Possible Answers:

The 3rd only

The 4th only

The 1st and 4th

The 1st and 3rd

Correct answer:

The 1st and 4th

Explanation:

The cosine is positive in the 1st and 4th quadrants and negative in 2nd and 3rd

Example Question #2 : How To Find Positive Cosine

Which of the following is equal to ?

Possible Answers:

Correct answer:

Explanation:

Here, we use the SOHCAHTOA ratios and the fact that csc x = 1 / sin x.

Cosine x = adjacent side length / hypotenuse length

Cosecant x = 1 / sin x = hypotenuse / opposite

(Adjacent / hypotenuse) * (hypotenuse / opposite) = Adjacent / opposite = Cotangent x.

Example Question #3 : How To Find Positive Cosine

 and  is between  and .  What is the value of ?

Possible Answers:

Correct answer:

Explanation:

For  to , we know that .  So, the question asks, what is the value of , where .  Therefore, it is asking what the value of  is, which is .

Example Question #4 : How To Find Positive Cosine

To the nearest , what is the cosine formed from the origin to ? Assume counterclockwise rotation.

Possible Answers:

Correct answer:

Explanation:

If the point to be reached is , then we may envision a right triangle with sides  and , and hypotenuse . The Pythagorean Theorem tells us that , so we plug in and find that: 

Thus, 

Now, SOHCAHTOA tells us that , so we know that:

Thus, our cosine is approximately .

Example Question #5 : How To Find Positive Cosine

Two drivers race to a finish line. Driver A drives north  blocks, and east  blocks and crosses the goal. Driver B drives the shortest direct route between the two points. Relative to east, what is the cosine of the angle at which Driver B raced? Round to the nearest .

Possible Answers:

Correct answer:

Explanation:

If the point to be reached is  blocks north and  blocks east, then we may envision a right triangle with sides  and , and hypotenuse . The Pythagorean Theorem tells us that , so we plug in and find that: 

Thus, 

Now, SOHCAHTOA tells us that , so we know that:

Thus, our cosine is approximately .

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