Working on the assumption that you are talking about a straight line graph

Standard equation form is: #y=mx+c#

#x# is the independent variable

#y# is the dependant variable (its value 'depends' on what you

assign to #x#

#m# is the gradient of the line (slope)

#color(white)(XXX)#going from left to right, a positive

#color(white)(XXX)#slop is upwards and a negative slope is downwards.

#c# is a constant value and is where the line intersects the y-axis.

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#color(blue)("To find the gradient:")#

The amount of up (or down) for the amount of along. That is:

#m=("change in the y-axis")/("change in the x-axis")#

Let #(x_1 ,y_1)-> (10,3)#

Let #x_2,y_2)->(-4,12)#

so #m= (y_2-y_1)/(x_2-x_1) -> (12-3)/((-4)-10) = 9/(-14)#

#color(blue)(m=-9/14)# which is negative so the line descends from left to right

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#color(blue)("To find the constant")#

We can substitute known value for #x# and #y# to find #c#

I am choosing #color(brown)((x_1 ,y_1)-> (10,3))#

So #y_1=mx_1+c# becomes:

#color(brown)(3=color(blue)(-9/14)(10)+color(black)(c))#

#c=3+(9xx10)/14#

#color(blue)(c=3+6 3/7= 9 3/7)#

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Putting it all together:

#y=-9/14 x + 9 3/7#