MTH 108 Lecture Notes - Lecture 31: Precalculus
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10. 1 systems of equations in two variables notes: sterling. Provide a generalization to each of the key terms listed in this section. Solve one of the two equations for either of the two variables in terms of the other variable. Substitute the solved expression into the other equation and solve for the rst variable. Substitute the rst solved variable into either expression and solve for the second vari- able. Substitution example x y = 9 x + y = 3. 9 + 2y 9 = 3 9. 2x + 5y = 18 x + 2y = 9 x + 2y 2y = 9 2y x = 9 2y. 18 + y 18 = 18 18 y = 36 x = 9 2y x = 9 2( 36) x = 9 + 72 x = 81 x + 2y = 9. 2x + 5y = 18 (81) + 2( 36) = 9 2(81) + 5( 36) = 18.