All SAT Math Resources
Example Questions
Example Question #1 : How To Find The Surface Area Of A Sphere
What is the surface area of a hemisphere with a diameter of ?
A hemisphere is half of a sphere. The surface area is broken into two parts: the spherical part and the circular base.
The surface area of a sphere is given by .
So the surface area of the spherical part of a hemisphere is .
The area of the circular base is given by . The radius to use is half the diameter, or 2 cm.
Example Question #9 : How To Find The Surface Area Of A Sphere
Six spheres have surface areas that form an arithmetic sequence. The two smallest spheres have radii 4 and 6. Give the surface area of the largest sphere.
The surface area of a sphere with radius can be determined using the formula
.
The smallest sphere, with radius , has surface area
The second-smallest sphere, with radius , has surface area
The surface areas are in an arithmetic sequence; their common difference is the difference of these two surface areas, or
Since the six surface areas are in an arithmetic sequence, the surface area of the largest of the six spheres - that is, the sixth-smallest sphere - is
Example Question #2 : How To Find The Surface Area Of A Sphere
The radii of six spheres form an arithmetic sequence. The smallest and largest spheres have radii 10 and 30, respectively. Give the surface area of the second-smallest sphere.
None of the other responses gives a correct answer.
The radii of the spheres form an arithmetic sequence, with
and
The common difference can be computed as follows:
The second-smallest sphere has radius
The surface area of a sphere with radius can be determined using the formula
.
Setting , we get
.
Example Question #791 : Geometry
Find the surface area of a sphere with radius 1.
To solve, use the formula for the surface are a of a sphere.
Substitute in the radius of one into the following equation.
Thus,
Example Question #16 : Spheres
Find the surface area of a sphere whose radius is 5.
To solve, simply use the formula for the surface area of a sphere. Thus,
Example Question #792 : Geometry
Find the surface area of a sphere with radius 4.
To solve, simply use the formula for the surface area of a sphere. Thus,
The surface area for a sphere is one of those formulas you are going to have to memorize. There isn't exactly an easy wasy to derive it. My only trick for differentiating it from other circular formulas is the fact that area is two-dimensional, so you only square the r, not cube it.
Example Question #795 : Geometry
The surface area of a given sphere is . What is the radius of the sphere?
The surface area of a given sphere is represented by the equation
Substituting in our given surface area, we can simplify this equation and solve for r.
Example Question #21 : Spheres
Find the surface area of a sphere whose radius is .
The equation for the surface area of a sphere is where represents the sphere's radius.
With our radius-value, we find:
Example Question #21 : Spheres
Give the area of the largest circle that can be drawn entirely on the surface of a sphere with surface area 720.
The circle of greatest size that can possibly be constructed on a sphere will have the same radius as the sphere as can be seen in the diagram below.
This circle has area
The surface area of a sphere is related to its radius by the formula
Since the surface area is 720,
If both sides are divided by 4, it can be seen that
making this the area of the circle.
Example Question #22 : Spheres
Let be a point on a sphere, and be the point on the sphere farthest from . The shortest distance from to along the surface is . Give the surface area of the sphere.
The diagram below shows the sphere with the points in question as well as the curve that connects them.
The curve connecting them is a semicircle whose radius coincides with that of the sphere. Given radius , a semicircle has length
Setting and solving for :
.
The surface area of a sphere, given its radius , is equal to
.
Setting :