Point-Slope Form

Thursday, November 4, 2010

Formula

• y – y1 = m(x – x1)– y1 is the y-coordinate– m is the slope– x1 is the x-coordinate

Graphing Using Point-Slope Form

• Graph the equation y – 5 = ½ (x – 2)– The equation shows that the line passes through

(2, 5) with slope of ½ .– Start at (2, 5). Using the slope, go up 1 unit and

right 2 units to (4,6). Draw a line through the two points.

• Graph the equation y – 5 = -⅔(x +2)

Writing an Equation in Point-Slope Form

• Write the equation of the line with the slope -3 that passes through the points (-1, 7).– Use the point-slope form• y – y1 = m(x – x1)

– Substitute (-1, 7) for (x1, y1) and -3 for m.• y – 7 = -3(x –(-1))• y – 7 = -3(x + 1)

• Write an equation of the line with slope ⅔ that passes through (10,-8).

• y + 8 = ⅔(x – 10)

• Write an equation of the line with slope 6 that passes through (3,-4).

• y + 4 = 6(x – 3)

• Write an equation of the line with slope 0 that passes through (-5, 2).

• y - 2 = 0(x + 5)• y – 2 = x + 5

Closure

• What is the formula for point-slope?– y – y1 = m(x – x1)

• What does each piece represent?– y1 is the y-coordinate– m is the slope– x1 is the x-coordinate