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The Equation of a Line Slope – Intercept form: y = mx + b ◦ Use when you are given the slope and (0, b) or if you are given the graph of the line. Point-Slope form: y – y1 = m(x – x1) ◦ Use when you are given the slope and (x, y) or if you are given 2 ordered pairs. ◦ Don’t leave your answer in the form, check the directions to see what’s required. 1. m = - ½ : (0, -4) 2. m = 2; (4, -2) 3. (-3,2) and (5, 7) Note: A, B, and C are integers, and A > 0 To write an equation in this form: 1. Rearrange so that the x and y terms are on the left and the constant is on the right. 2. If needed, multiply everything by the LCD to clear any fractions. 3. If needed, multiply everything by -1 so the coefficient of x is positive. 1. (1, 3) and (-2, -9) 2. (-5, -2) and (6, -4) Parallel lines have equal slopes. Symbol: || Perpendicular lines have opposite reciprocal slopes. Symbol: | Ex: are the 2 lines ||, | , or neither? 6x – 2y = 7 x + 3y = -5 Write the equation of the line that passes through the given point and is parallel to the given equation: (-1, 1); y = -3x + 1 Write the equation of the line that passes through the given point and is perpendicular to the given equation: (2, 8); x + 2y = 9