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Example Questions
Example Question #221 : Coordinate Geometry
What is the value of the -intercept for the line given below?
The x-intercept is where the line crosses the x-axis. In other words,
This gives:
Subtracting 98 from both sides gives:
Dividing both sides by 14 gives the final answer:
Example Question #602 : Geometry
Give the area of the triangle on the coordinate plane that is bounded by the -axis, and the lines of the equations
and
It is necessary to find the vertices of the triangle, each of which is a point at which two of the three lines intersect.
The intersection of the -axis - the line
- and the line of the equation
, is found by noting that if
, then, by substitution,
; this point of intersection is at
, the origin.
The intersection of the -axis and the line of the equation
is found similarly:
This intersection point is at .
The intersection of the lines with equations and
can be found using the substitution method, setting
in the latter equation and solving for
:
Since ,
, making
the point of intersection.
The vertices are at .
The lines in question are graphed below, and the triangle they bound is shaded:
If we take the horizontal side as the base, its length is seen to be the -coordinate of the
-intercept,
; its (vertical) height is the
-coordinate of the opposite vertex,
. The area is half the product of the two, or
Example Question #22 : How To Find X Or Y Intercept
Given the line , what is the sum of the
-intercept and the
-intercept?
Intercepts occur when a line crosses the -axis or the
-axis. When the line crosses the
-axis, then
and
. When the line crosses the
-axis, then
and
. The intercept points are
and
. So the
-intercept is
and the
intercept is
and the sum is
.
Example Question #31 : X And Y Intercept
Where does the line given by intercept the
-axis?
First, put in slope-intercept form.
.
To find the -intercept, set
and solve for
.
Example Question #32 : X And Y Intercept
Where does the graph of 2x + 3y = 15 cross the x-axis?
(0, 5)
(0, 0)
(7.5, 0)
(0, -5)
(-7.5, 0)
(7.5, 0)
To find the x-intercept, set y=0 and solve for x. This gives an answer of x = 7.5.
Example Question #1 : How To Find The Equation Of A Circle
If the center of a circle is at (0,4) and the diameter of the circle is 6, what is the equation of that circle?
x2 + y2 = 9
(x-4)2 + y2 = 9
x2 + (y-4)2 = 36
(x-4)2 + y2 = 36
x2 + (y-4)2 = 9
x2 + (y-4)2 = 9
The formula for the equation of a circle is:
(x-h) 2 + (y-k)2 = r2
Where (h,k) is the center of the circle.
h = 0 and k = 4
and diameter = 6 therefore radius = 3
(x-0) 2 + (y-4)2 = 32
x2 + (y-4)2 = 9
Example Question #1 : How To Find The Equation Of A Circle
Circle A is given by the equation (x – 4)2 + (y + 3)2 = 29. Circle A is shifted up five units and left by six units. Then, its radius is doubled. What is the new equation for circle A?
(x – 10)2 + (y + 8)2 = 58
(x – 10)2 + (y + 8)2 = 116
(x + 2)2 + (y – 2)2 = 58
(x + 2)2 + (y – 2)2 = 116
(x – 2)2 + (y + 2)2 = 58
(x + 2)2 + (y – 2)2 = 116
The general equation of a circle is (x – h)2 + (y – k)2 = r2, where (h, k) represents the location of the circle's center, and r represents the length of its radius.
Circle A first has the equation of (x – 4)2 + (y + 3)2 = 29. This means that its center must be located at (4, –3), and its radius is √29.
We are then told that circle A is shifted up five units and then left by six units. This means that the y-coordinate of the center would increase by five, and the x-coordinate of the center would decrease by 6. Thus, the new center would be located at (4 – 6, –3 + 5), or (–2, 2).
We are then told that the radius of circle A is doubled, which means its new radius is 2√29.
Now, that we have circle A's new center and radius, we can write its general equation using (x – h)2 + (y – k)2 = r2.
(x – (–2))2 + (y – 2)2 = (2√29)2 = 22(√29)2 = 4(29) = 116.
(x + 2)2 + (y – 2)2 = 116.
The answer is (x + 2)2 + (y – 2)2 = 116.
Example Question #1 : Circles
Which of the following equations describes all the points (x, y) in a coordinate plane that are five units away from the point (–3, 6)?
y + 6 = 5 – (x – 3)2
(x – 3)2 + (y + 6)2 = 25
(x – 3)2 + (y + 6)2 = 5
(x + 3)2 + (y – 6)2 = 25
(x – 3)2 – (y + 6)2 = 25
(x + 3)2 + (y – 6)2 = 25
We are trying to find an equation for all of the points that are the same distance (5 units) from (–3, 6). The locus of all points equidistant from a single point is a circle. In other words, we need to find an equation of a circle. The center of the circle will be (–3, 6), and the radius, which is the distance from (–3,6), will be 5.
The standard form of a circle is given below:
(x – h)2 + (y – k)2 = r2, where the center is located at (h, k) and r is the length of the radius.
In this case, h will be –3, k will be 6, and r will be 5.
(x – (–3))2 + (y – 6)2 = 52
(x + 3)2 + (y – 6)2 = 25
The answer is (x + 3)2 + (y – 6)2 = 25.
Example Question #1 : Circles
What is the equation for a circle of radius 12, centered at the intersection of the two lines:
y1 = 4x + 3
and
y2 = 5x + 44?
(x - 41)2 + (y - 161)2 = 144
(x - 22)2 + (y - 3)2 = 12
(x - 3)2 + (y - 44)2 = 144
(x + 41)2 + (y + 161)2 = 144
None of the other answers
(x + 41)2 + (y + 161)2 = 144
To begin, let us determine the point of intersection of these two lines by setting the equations equal to each other:
4x + 3 = 5x + 44; 3 = x + 44; –41 = x
To find the y-coordinate, substitute into one of the equations. Let's use y1:
y = 4 * –41 + 3 = –164 + 3 = –161
The center of our circle is therefore: (–41, –161).
Now, recall that the general form for a circle with center at (x0, y0) is:
(x - x0)2 + (y - y0)2 = r2
For our data, this means that our equation is:
(x + 41)2 + (y + 161)2 = 122 or (x + 41)2 + (y + 161)2 = 144
Example Question #1 : Circles
The diameter of a circle has endpoints at points (2, 10) and (–8, –14). Which of the following points does NOT lie on the circle?
(2, –14)
(–8, 10)
(–15, –7)
(9,3)
(–8,–12)
(–8,–12)
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