2.5.2 – Writing Equations of Lines Cont’d

2.5.2 – Writing Equations of Lines Cont’d

Yesterday, we could write equations of lines in a few ways • 1) Given slope and y-intercept (y = mx + b) • 2) Given a graph of a line, determine slope and y-intercept (also write in y = mx + b) • 3) Use point-slope form given any point and slope of a line (y - y1 = m(x - x1)) • Could write in y = mx + b as well if we simplified it

We’ll start off still using point-slope form, but this time in a different scenario • Remember, only need 2 points to represent a line • Now, you will be given two points, and you will need to find an equation of that line

2 points • Using two points, we will; • 1) Find the slope, using the slope formula; m = • 2) Using any of the two points, write in point-slope form • 3) Simplify as y = mx + b

Example. Write an equation of the line that passes through the points (-2, 3) and (2, -5). • Slope = m = • Point-Slope form; • Slope-Intercept form;

Example. Write an equation of the line that passes through the points (-8, 10) and (-2, 17). • Slope = m = • Point-Slope form; • Slope-Intercept form;

Graphically • Similar to yesterday, you can determine the equation of a line graphically, even if we cannot accurately locate the y-intercept • Just find two known points, then • 1) Find the slope using rise/run (counting) • 2) Pick one point, use point-slope formula

Example. Write an equation of the line shown.

Parallel/Perpendicular Equations • Recall, we covered parallel and perpendicular lines • What determines if two lines are parallel? • What determines if two lines are perpendicular? • Using given info, we will once again use point-slope form after finding each slope

Example. Write an equation of the line that is parallel to y = 4x – 5 and goes through the point (-1, 3).

Example. Write an equation of the line that is perpendicular to y = 4x – 5 and goes through the point (-1, 3).

Assignment • Pg. 98 • 24, 34-52 even, 59, 60 • Pg. 100 • 11-13

2.5.2 – Writing Equations of Lines Cont’d