HiSET: Math : Cones

Study concepts, example questions & explanations for HiSET: Math

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Example Questions

Example Question #11 : Cones

About the y-axis, rotate the triangle formed with the x-axis, the y-axis, and the line of the equation

.

Give the volume of the solid of revolution formed.

Possible Answers:

None of the other choices gives the correct response.

Correct answer:

Explanation:

The vertices of the triangle are the points of intersection of the three lines. The -axis and the -axis meet at the origin .

The point of intersection of the -axis and the graph of - the -intercept of the latter - can be found by substituting 0 for :

Divide both sides by 2 to isolate :

The point of intersection is at .

Similarly, The point of intersection of the -axis and the graph of - the -intercept of the latter - can be found by substituting 0 for :

The point of intersection is at .

The three vertices of the triangle are at the origin, , and . When this triangle is rotated about the -axis, the resulting solid of revolution is a cone whose base has radius , and which has height . Substitute these values into the formula for the volume of a cone:

Example Question #181 : Hi Set: High School Equivalency Test: Math

A right cone has slant height 20; its base has radius 10. Which of the following gives its volume to the nearest whole number?

(Round to the nearest whole number).

Possible Answers:

Correct answer:

Explanation:

The volume of a cone, given radius and height , can be calculated using the formula

.

We are given that , but we are not given the value of . We are given slant height , and since the cone is a right cone, its radius, height, and slant height can be related using the Pythagorean relation

.

Substituting 10 for and 20 for , we can find :

Now substitute in the volume formula:

To the nearest whole, this is 1,814.

Example Question #13 : Cones

The volume of a cone is . Which of the following most closely approximates the radius of the base of the cone if its height is ?

Possible Answers:

Correct answer:

Explanation:

The volume of a cone is given by the formula 

We are given that . Thus, the volume of our cone is given by

.

We are given that the volume of our cone is .

Thus,

so

and

.

Thus, 

.

so the correct answer is .

 

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