All HiSET: Math Resources
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.
None of the other choices gives the correct response.
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).
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 ?
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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