Answer:
The intercepts of a graph are points at which the graph crosses the axes. The x-intercept is the point at which the graph crosses the x-axis. At this point, the y-coordinate is zero. The y-intercept is the point at which the graph crosses the y-axis. At this point, the x-coordinate is zero.
To determine the x-intercept, we set y equal to zero and solve for x. Similarly, to determine the y-intercept, we set x equal to zero and solve for y. For example, lets find the intercepts of the equation \displaystyle y=3x - 1y=3x−1.
To find the x-intercept, set \displaystyle y=0y=0.
y
=
3
x
−
1
0
=
3
x
−
1
1
=
3
x
1
3
=
x
(
1
3
,
0
)
x
-intercept
To find the y-intercept, set \displaystyle x=0x=0.
y
=
3
x
−
1
y
=
3
(
0
)
−
1
y
=
−
1
(
0
,
−
1
)
y
-intercept
We can confirm that our results make sense by observing a graph of the equation as in Figure 10. Notice that the graph crosses the axes where we predicted it would.
This is an image of a line graph on an x, y coordinate plane. The x and y-axis range from negative 4 to 4. The function y = 3x – 1 is plotted on the coordinate plane
Figure 12
HOW TO: GIVEN AN EQUATION, FIND THE INTERCEPTS.
Find the x-intercept by setting \displaystyle y=0y=0 and solving for \displaystyle xx.
Find the y-intercept by setting \displaystyle x=0x=0 and solving for \displaystyle yy.
EXAMPLE 4: FINDING THE INTERCEPTS OF THE GIVEN EQUATION
Find the intercepts of the equation \displaystyle y=-3x - 4y=−3x−4. Then sketch the graph using only the intercepts.
SOLUTION
Set \displaystyle y=0y=0 to find the x-intercept.
y
=
−
3
x
−
4
0
=
−
3
x
−
4
4
=
−
3
x
−
4
3
=
x
(
−
4
3
,
0
)
x
-intercept
Set \displaystyle x=0x=0 to find the y-intercept.
y
=
−
3
x
−
4
y
=
−
3
(
0
)
−
4
y
=
−
4
(
0
,
−
4
)
y
-intercept
Plot both points, and draw a line passing through them as in Figure 11.
This is an image of a line graph on an x, y coordinate plane. The x-axis ranges from negative 5 to 5. The y-axis ranges from negative 6 to 3. The line passes through the points (-4/3, 0) and (0, -4).
Figure 13
