4d+Finding+Equations+of+Lines

[|Purplemath: Finding Equation of the Line] __Find the Equation of a Line:__ Remember slope intercept form is //y=mx+b// //1.// Find the slope (if a problem is not already in slope-intercept form: //y= mx+b//). Indirect slopes are in the form of: - parallel to another line - perpendicular to another line -through two given points 2. Substitute given coordinate points (using information) for //x, y, and m//. Solve for //b (y-intercept)// 3. Write your new equations with the __new__ values, you found for m and b. Example: y= -2x + 7 Examples in Calculations: 1. Find the Equation of a line that is __perpendicular__ to y = 3//x// + 4 and passes through the point ( 6, -9 ). Express your answer in slope intercept form. Perpendicular: Reciprocal; opposite. So, the slope would like this (because it is flipped): m = -1/3 y = -1/3x + b (Insert given points): -9 = -1/3 (6) + b -9 = -2 + b +2 +2 (The two's cancel)  -7 = b   Final Answer: y = -1/3x - 7   2nd Example: __Find the Equation of the line that passes through the points (8, -3) and (-4, -9)--->Either point works when inserting into equation. Express your answer in slope intercept form.   __You have to find the slope of the two points. So, use: __ m= __   ____ m= __ __ y = 1/2x + b