Assumption: This is for a strait line graph (not stated in question)
Let #(x_1,y_1) -> (8,2)#
Let #(x_2,y_2) -> (5,8)#
Using standard equation for strait line graph.
#y=mx+c#.............(1)
#color(green)("Method: determine gradient(m) Then substitute in equation (1) with")#
#color(green)("known values for x and y to determine the constant's value.")#
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#color(blue)("To find the gradient")#
gradient # =m =("change in Up or down")/("change in along") #
#color(brown)(m)=(y_2-y_1)/(c_2-x_1)=(8-2)/(5-8) = 6/(-3)= color(brown)(-2)color(white)(...)#.......(2)
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#color(blue)("To find the value of c")#
Substitute for m and#color(white)(.) (x_1,y_1)# into equation (1)
#2=(-2)(8)+c#
#color(brown)(c= 18)#
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#color(blue)("Bring it all together")#
#color(brown)(y= (-2)x+18)#
#color(green)("Note: as the gradient is negative it is a downward slope")#
#color(green)("as you move from left to right.")#
