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the slope of the straight line can be expressed as (B.10) Note that m and b can have either positive or negative values. If m ' 0, the straight line has a positive slope, as in Figure B.1. If m ( 0, the straight line has a negative slope. Exercises 1. Draw graphs of the following straight lines: (a) y # 5x $ 3 (b) y # "2x $ 4 (c) y # "3x " 6 2. Find the slopes of the straight lines described in Exercise 1. Answers (a) 5 (b) " 2 (c) " 3 (a) (0, "4) and (4, 2) (b) (0, 0) and (2, " 5) (c) (" 5, 2) and (4, " 2) Answers (a) 3/2 (b) " 5/2 (c) " 4/9 Solving Simultaneous Linear Equations Consider the equation 3x $ 5y # 15, which has two unknowns, x and y. Such an equa- If a problem has two unknowns, a unique solution is possible only if we have two equations. In general, if a problem has n unknowns, its solution requires n equations. In Slope # y
2 " y 1 x
2 " x 1 # ) y ) x A.18 Appendix B • Mathematics Review Example 2 y (1) (2) (3) m > 0 b < 0 m < 0 b > 0 m < 0 b < 0 x Figure B.2 Two linear equations containing two unknowns can also be solved by a graphical method. If the straight lines corresponding to the two equations are plotted in a con- x " 2y # "1 x " y # 2 Solve the following two simultaneous equations: Solution From Equation (2), x # y $ 2. Substitution of this " 1 x # y $ 2 # " 3 y # 6y # "18 5(y $ 2) $ y # "8 (2)
2x " 2y # 4 (1) 5x $ y # "8 Alternate Solution Multiply each term in Equation (1) by " 3 y # x " 2 # " 1 x # 12x # "12 2x " 2y # 4 10x $ 2y # "16 |