Step 1: Note down the given points as well as assign these points with the variables

            EXAMPLE: ( 7, 4 ) assign this point with (x_1, y_1)

                              ( 2, 0 ) assign this point with (x_2,y_2)

                      ................etc

Step 2: Calculate gradient or slope(m) from two points

            FORMULA: \frac{y-change}{x-change},

                            or \frac{y_2 - y_1}{x_2 - x_1}

            EXAMPLE: Slope of A(7, 4) and B(2, 0 )

                              \frac{4-0}{7-2} = \frac{4}{5}

Step 3: Find the slope of the another line.

        NOTE: i) Parallel lines have the same slope.

                    ii) Perpendicular lines have slopes that are opposite reciprocals, like

                       \frac{a}{b} \text{ and } \frac{-b}{a}. The slopes also have a product of -1

Step 4: Substitute either values slope(m) and any one point into the equation of a straight line.

            FORMULA: Equation of a straight line

                               y - y_1 = m(x - x_1)

                            Where m = slope and ( x_1, y_1) = any point

            EXAMPLE: I took (2, 0) as a point and m = \frac{4}{5}

                                         y - 0 = \frac{4}{5} ( x - 2)

                                            5y = 4x - 8

Step 4: Simplify and make the equation in the form of Ax + By + C =0

b) Find the exact x-coordinate of E.

Step 1: Take the calculated line equation of the of the perpendicular line

Step 2: Notice the coordinate from the diagram and substitute in the line equation to get the another coordinate.

NOTE: From the diagram AB line parallel to the x-axis at y = 7. Hence, any point on the line has same y coordinator. So substitute y = 7 in the line equation to get the x-coordinator

Step 3: Simplify the equation

Apply the BODMAS rules