How do you graph #y=-9x#?

Given:# y=-9x#

As the number in front of #x# (coefficient of #x#) is negative it means that the line slopes downward as you read left to right on the x-axis.

The graph crosses (intercepts) the x-axis at y=0
and crosses (intercepts) the y-axis as x=0.

Set y=0 giving: #" "0=-9x => x=0#
So x-intercept# ->(x,y)=(0,0)#

Set x=0 giving: #" "y=-9xx0 =>y=0#
So y-intercept #->(x,y)=(0,0)#

This demonstrates that the strait line passes through the origin.
The origin is where the two axis cross. So this gives us the first point:

Let the first point be #P_1->(x_1,y_1)=(0,0)#

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All we need know is a second point. This may be determined by substituting any value you so chose into #x#

I chose #x->3#

So we have: #y=-9x" "->" "y=-(9)xx3 = -27#

Let the second point be# P_2->(x_2,y_2)=(3,-27)#
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Put a dot at each of these points and draw a strait line through them. Extend this line to the edge of the graph region.