How to find x or y intercept - ACT Math

Card 0 of 16

Question

In the standard (x, y) coordinate plane, a circle has the equation . At what points does the circle intersect the x-axis?

Answer

The generic equation of a circle is (x - x0)2 + (y - y0)2 = r2, where (x0, y0) are the coordinates of the center and r is the radius.

In this case, the circle is centered at the origin with a radius of 8. Therefore the circle hits all points that are a distance of 8 from the origin, which results in coordinates of (8,0) and (-8,0) on the x-axis.

Act_math_172_01

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Question

What is the y-intercept of a line that passes through the point with slope of ?

Answer

Point-slope form follows the format y - y1 = m(x - x1).

Using the given point and slope, we can use this formula to get the equation y - 8 = -2(x + 5).

From here, we can find the y-intercept by setting x equal to zero and solving.

y - 8 = -2(0 + 5)

y - 8 = -2(5) = -10

y = -2

Our y-intercept will be (0,-2).

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Question

Given the linear equation below, what are the x- and y-intercepts_,_ respectively?

Answer

To find the x-intercept we will need to plug in zero for the y-value.

The x-intercept will be .

To find the y-intercept we will need to plug in zero for the x-value.

The y-intercept will be .

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Question

What are the y and x intercepts of the given equation, respectively?

y = 2x – 2

Answer

The equation is already in slope-intercept form. The y-intercept is (0, –2). Plug in 0 for y and we get the x intercept of (1, 0)

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Question

What is the x-intercept of the following line?

y = –3_x_ + 12

Answer

The x-intercept occurs when the y-coordinate = 0.

y = –3_x_ + 12

0 = –3_x_ + 12

3_x_ = 12

x = 12/3 = 4

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Question

What is the \dpi{100} \small x-coordinate of the point in the standard \dpi{100} \small (x,y) coordinate plane at which the two lines \dpi{100} \small y=4x+8 and \dpi{100} \small y=3x-7 intersect?

Answer

\dpi{100} \small 4x+8=3x-7

\dpi{100} \small x+8=-7

\dpi{100} \small x=-15

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Question

At what point do the lines \small y=\frac{1}{4}x+7 and \small y=4x + 7 intersect?

Answer

Short way:

The lines intersect somewhere because they have different slopes. Because they have the same y-intercept, they must intersect at that point.

Long way using substitution:

\small y=\frac{1}{4}x+7

\small y-7 = \frac{1}{4}x

\small x = 4y - 28

Plug this into \small y=-4x+7

\small y=-4(4y-28)+7

\small y=-16y+112+7

\small 17y=119

\small y=7

Find \small x

\small x=4(7)-28=0

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Question

What is the -intercept of the line in the standard coordinate plane that goes through the points and ?

Answer

The answer is .

The slope of the line is determined by calculating the change in over the change in .

The point-slope form of the equation for the line is then

. The -intercept is determined by setting and solving for . This simplifies to which shows that is the -interecept.

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Question

What are the and -intercepts of the line defined by the equation:

Answer

To find the intercepts of a line, we must set the and values equal to zero and then solve.

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Question

Find the -intercept(s) for the following equation:

Answer

To find the intercepts, is set equal to . This yields:

And finally

It is important to realize that both and must be included because is also equal to . Finally, these are put into their point forms, and .

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Question

What is the largest x-intercept of ?

Answer

To find the x-intercepts of an equation, you can just set the y value of the equation equal to zero. Thus you get, for our data:

Now, you can divide everything by to simplify your equation:

Luckily, this is an easy equation to factor:

Based on this, you know that the two intercepts must be where and . Thus, the largest intercept is .

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Question

What is the sum of the x-intercepts of ?

Answer

To find the x-intercepts of an equation, you can set its y value equal to zero. Thus, you get for our equation:

Now, factor out all common factors:

From this, you can further factor:

Thus, the x-intercepts of our equation are ,, and . The sum of these values is .

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Question

What is the of the following equation: ?

Answer

The y-intercept is the constant at the end of the equation. Thus for our equation the y-intercept is 7

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Question

What is the -intercept of the following linear equation:
?

Give your answer as an ordered pair.

Answer

The x-intercept is the value of the linear equation with y = 0 (this means the line will be on the x-axis when y is zero).

Thus we plug 0 in for y and solve for x.

.

Now put it in an ordered pair, remember y = 0:

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Question

What is the and intercepts of the linear equation given by:
?

Answer

To find the and intercept of a linear equation, find the points where and are equal to zero.

To do this, plug in zero for either variable and then solve for the other.

this yields:

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Question

What is the and intercepts of the following linear equation:

Answer

To find the and intercepts of an equation, set each variable to zero (one at a time) and solve for the other variable.

Next, set to zero:


Now put these two sets of points into two ordered pairs:

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