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Sagot :
Given:
A line passes through the points (-1, -1) and (5,8).
To find:
Which points lie on the same line?
Solution:
If a line passes through two points, then the equation of the line is:
[tex]y-y_1=\dfrac{y_2-y_1}{x_2-x_1}(x-x_1)[/tex]
A line passes through the points (-1, -1) and (5,8). So, the equation of the line is:
[tex]y-(-1)=\dfrac{8-(-1)}{5-(-1)}(x-(-1))[/tex]
[tex]y+1=\dfrac{8+1}{5+1}(x+1)[/tex]
[tex]y+1=\dfrac{9}{6}(x+1)[/tex]
[tex]y+1=\dfrac{3}{2}(x+1)[/tex]
Multiply both sides by 2.
[tex]2(y+1)=3(x+1)[/tex]
[tex]2y+2=3x+3[/tex]
[tex]2y=3x+3-2[/tex]
[tex]y=\dfrac{3}{2}x+\dfrac{1}{2}[/tex]
So, the equation of the line is [tex]y=\dfrac{3}{2}x+\dfrac{1}{2}[/tex].
Now, check each point for this equation.
Putting [tex]x=-3[/tex], we get
[tex]y=\dfrac{3}{2}(-3)+\dfrac{1}{2}[/tex]
[tex]y=\dfrac{-9+1}{2}[/tex]
[tex]y=\dfrac{-8}{2}[/tex]
[tex]y=-4[/tex]
Similarly,
For [tex]x=9,y=15[/tex].
For [tex]x=1,y=2[/tex].
For [tex]x=4,y=6.5[/tex].
For [tex]x=3,y=5[/tex].
For [tex]x=-2,y=-2.5[/tex].
Therefore, the points (-3,-4), (9,14), (1,2) and (3,5) lie on the same line but the points (4,7) and (-2,-2) are not on that line.
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