The line AB has equation 5x + 3y + 3 = 0. The point with coordinates (2k + 3, 4 -3k) lies on the line AB. How do you find the value of k.

This kind of question requires correct substitution by setting the x in the original equation equal to the x value of the point ( 2k+3) and setting the y value of the original equation to the y value of the point (4-3k). This gives the equation:5(2k+3) + 3(4-3k) + 3 = 0This expands out to equal : 10k + 15 + 12 - 9k + 3 =0This can be simplified to the equation : k = -30.For these type of questions it is good to show each stage of working out in the exam just in case you might make an error somewhere, then they can still give you working out marks.