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To draw the lines more easily, write the equations in slope-intercept form.
Graph:
Figure: It looks like a square.
We are given four equations in standard form in the same coordinate plane. x+4y=8 4x-y=-1 x+4y=- 12 4x-y=20 We want to draw their graphs and find out what figure these four lines form. We will do this by following two steps.
LHS-x=RHS-x
.LHS /4.=.RHS /4.
Write as a difference of fractions
Calculate quotient
Commutative Property of Addition
a/b=1/b* a
Equations in Standard From | Equations in Slope-Intercept Form |
---|---|
x+4y=8 | y=- 1/4x+2 |
4x-y=-1 | y=4x+1 |
x+4y=- 12 | y=- 1/4x-3 |
4x-y=20 | y=4x-20 |
We are ready to draw the graphs of the equations!
We will draw y=- 14x+2 by using its y-intercept and its slope.
With the same procedure we will draw the other lines.
For further information we will check the slopes and side lengths. We will follow three steps.
We will begin by checking the slopes.
To find the figure that four lines form we will use the slopes of the lines. Let's look at the slope-intercept form of the given equations and examine their slopes.
Equations in Slope-Intercept Form | Slopes |
---|---|
y=- 1/4x+2 | - 1/4 |
y=4x+1 | 4 |
y=- 1/4x-3 | - 1/4 |
y=4x-20 | 4 |
Recall that the slopes of perpendicular lines are opposite reciprocals, and the slopes of parallel lines are the same.
Since all four angles of the quadrilateral are right angles, this figure is a rectangle. Now we will investigate whether the given figure is a square.
(II): y= 33/17
(II): LHS-1=RHS-1
(II): Write as a fraction
(II): Subtract fractions
(II): .LHS /4.=.RHS /4.
(II): Rearrange equation
Pairs of Equations | Intersection Points |
---|---|
y=- 1/4x+2 and y=4x+1 | (4/17,33/17) |
y=- 1/4x+2 and y=4x-20 | (88/17, 12/17) |
y=- 1/4x-3 and y=4x+1 | (- 16/17,- 47/17) |
y=- 1/4x-3 and y=4x-20 | (4,- 4) |
As we found the points of all vertices of the figure, now we can find the side lengths.
Points | Distance Formula | Side Lengths |
---|---|---|
(4/17,33/17) and (88/17,12/17) | d = sqrt((88/17-4/17)^2+(12/17-33/17)^2) | ≈ 5.09 |
(- 16/17,- 47/17) and (4,- 4) | d = sqrt((- 16/17-4)^2+(- 47/17-(- 4))^2) | ≈ 5.09 |
(4/17,33/17) and (- 16/17,- 47/17) | d = sqrt((88/17-(- 16/17))^2+(12/17-(- 47/17))^2) | ≈ 4.85 |
(88/17,12/17) and (4,- 4) | d = sqrt((88/17-4)^2+(12/17-(- 4))^2) | ≈ 4.85 |
We will show the side lengths in the graph, as well.
As all four sides of the quadrilateral are not equal, these figure is not a square. It is a rectangle.