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No.049 Find the Equation from a Graph

POINT
① Choose one easy-to-read point (x, y) on the graph.
② Substitute its coordinates into y = ax to find a, then write the equation.
Example
Find the equation of each graph in the form y = ax.
①
xyO-5-5-4-4-3-3-2-2-1-11122334455(2, 4)
②
xyO-5-5-4-4-3-3-2-2-1-11122334455(5, -3)
Watch. Think. Try.

Try it yourself.

Use a clear point on each graph to find a. Then write the equation in the form y = ax.

01
Find the equation of the graph in the form y = ax.
xyO-5-5-4-4-3-3-2-2-1-11122334455(1, 3)
y = 3x
Using the point (1, 3):   3 = 1a   →   a = 3
02
Find the equation of the graph in the form y = ax.
xyO-5-5-4-4-3-3-2-2-1-11122334455(2, -4)
y = −2x
Using the point (2, -4):   -4 = 2a   →   a = -2
03
Find the equation of the graph in the form y = ax.
xyO-5-5-4-4-3-3-2-2-1-11122334455(4, 2)
y = 1/2 x
Using the point (4, 2):   2 = 4a   →   a = 1/2
04
Find the equation of the graph in the form y = ax.
xyO-5-5-4-4-3-3-2-2-1-11122334455(-4, 2)
y = −1/2 x
Using the point (-4, 2):   2 = -4a   →   a = -1/2
05
Find the equation of the graph in the form y = ax.
xyO-5-5-4-4-3-3-2-2-1-11122334455(3, 4)
y = 4/3 x
Using the point (3, 4):   4 = 3a   →   a = 4/3
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