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Solving Systems of Equations The Elimination Method Objectives • Learn the procedure of the Elimination Method using addition • Learn the procedure of the Elimination Method using multiplication • Solving systems of equations using the Elimination Method Elimination using Addition Consider the system x - 2y = 5 2x + 2y = 7 Lets add both equations to each other REMEMBER: We are trying to find the Point of Intersection. (x, y) Elimination using Addition Consider the system x - 2y = 5 + 2x + 2y = 7 Lets add both equations to each other NOTE: We use the Elimination Method, if we can immediately cancel out two like terms. Elimination using Addition Consider the system x - 2y = 5 + 2x + 2y = 7 = 12 3x x=4 Lets add both equations to each other ANS: (4, y) NOTE: We use the Elimination Method, if we can immediately cancel out two like terms. Elimination using Addition Consider the system x - 2y = 5 2x + 2y = 7 4 - 2y = 5 - 2y = 1 y= 1 2 Lets substitute x = 4 into this equation. Solve for y ANS: (4, y) NOTE: We use the Elimination Method, if we can immediately cancel out two like terms. Elimination using Addition Consider the system x - 2y = 5 2x + 2y = 7 4 - 2y = 5 - 2y = 1 y= 1 2 Lets substitute x = 4 into this equation. Solve for y 1 ANS: (4, 2 ) NOTE: We use the Elimination Method, if we can immediately cancel out two like terms. Elimination using Addition Consider the system 3x + y = 14 4x - y = 7 NOTE: We use the Elimination Method, if we can immediately cancel out two like terms. Elimination using Addition Consider the system 3x + y = 14 + 4x - y = 7 7x = 21 x=3 ANS: (3, y) Elimination using Addition Consider the system 3x + y = 14 Substitute x = 3 into this equation 4x - y = 7 3(3) + y = 14 9 + y = 14 y=5 ANS: (3, 5 ) NOTE: We use the Elimination Method, if we can immediately cancel out two like terms. Examples… 1. 2x + y = 5 3x y = 15 ANS: (4, -3) 2. 6y + x = 11 2y x = 5 ANS: (-1, 2) Elimination using Multiplication Consider the system 6x + 11y = -5 6x + 9y = -3 Elimination using Multiplication Consider the system + 6x + 11y = -5 6x + 9y = -3 12x + 20y = -8 When we add equations together, nothing cancels out Elimination using Multiplication Consider the system 6x + 11y = -5 6x + 9y = -3 Elimination using Multiplication Consider the system -1 (6x + 11y = -5 ) 6x + 9y = -3 Elimination using Multiplication Consider the system + - 6x - 11y = 5 6x + 9y = -3 -2y = 2 y = -1 ANS: (x, -1 ) Elimination using Multiplication Consider the system 6x + 11y = -5 6x + 9y = -3 Lets substitute y = -1 into this equation y = -1 6x + 9(-1) = -3 6x + -9 = -3 +9 +9 6x = 6 x=1 ANS: (x, -1 ) Elimination using Multiplication Consider the system 6x + 11y = -5 6x + 9y = -3 Lets substitute y = -1 into this equation y = -1 6x + 9(-1) = -3 6x + -9 = -3 +9 +9 6x = 6 x=1 ANS: ( 1, -1 ) Elimination using Multiplication Consider the system x + 2y = 6 3x + 3y = -6 Multiply by -3 to eliminate the x term Elimination using Multiplication Consider the system -3 ( x + 2y = 6 ) 3x + 3y = -6 Elimination using Multiplication Consider the system + -3x + -6y = -18 3x + 3y = -6 -3y = -24 y=8 ANS: (x, 8) Elimination using Multiplication Consider the system x + 2y = 6 3x + 3y = -6 Substitute y =14 into equation y =8 x + 2(8) = 6 x + 16 = 6 x = -10 ANS: (x, 8) Elimination using Multiplication Consider the system x + 2y = 6 3x + 3y = -6 Substitute y =14 into equation y =8 x + 2(8) = 6 x + 16 = 6 x = -10 ANS: (-10 , 8) Examples 1. x + 2y = 5 2. x + 2y = 4 2x + 6y = 12 x - 4y = 16 ANS: (3, 1) ANS: (8, -2) More complex Problems Consider the system 3x + 4y = -25 2x - 3y = 6 Multiply by 2 Multiply by -3 More complex Problems Consider the system 2( 3x + 4y = -25 ) -3( 2x - 3y = 6) More complex Problems Consider the system + 6x + 8y = -50 -6x + 9y = -18 17y = -68 y = -4 ANS: (x, -4) More complex Problems Consider the system 3x + 4y = -25 2x - 3y = 6 2x - 3(-4) = 6 2x - -12 = 6 2x + 12 = 6 2x = -6 Substitute y = -4 x = -3 ANS: (x, -4) More complex Problems Consider the system 3x + 4y = -25 2x - 3y = 6 2x - 3(-4) = 6 2x - -12 = 6 2x + 12 = 6 2x = -6 Substitute y = -4 x = -3 ANS: ( -3 , -4) Examples… 2. 1. 4x + y = 9 2x + 3y = 1 3x + 2y = 8 5x + 7y = 3 ANS: (2, 1) ANS: (2, -1)