(i) Find the gradient of the straight line passing through the points: (0,3) and (9,21). (ii) Write down the equation of the line in form y = mx + c

(i) To find the gradient of a straight light, we take any two (different) points on the straight line and compute the change in Y divided by the change in X. So here this is; (21-3)/(9-0) = 18/9 = 2. So the grandient is +2. (ii) To put the straight line into the form y=mx+c, we first note that 'm' is the gradient, and so is 2. Then, we substitute values for 'y' and 'x' using any one of our points. So at the point '(0,3)' we have x=0 and y=3. So we have 3=0*2 + c, so c =3. Therefore we have y=2x +3!