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# Equations of straight lines

When working with straight lines, there are often many ways to arrive at an equation. Let's see:

Slope Intercept Form
(if you know the slope and where the
line crosses the y-axis, use this form) y = mx + b

m = slope
b = y-intercept
(where line crosses the y-axis.)

Point Slope Form
(if you know a point and the slope,
use this form)  m = slope = any point on the line.

and...

Find the equation of the line that goes through two points P(x 1,x2) and Q(y1,y2)
Firts find the slope using
and then use the formula: Write the slope-intercept form of the equation of the line with the slope 2 that contains the point (-4,-5).
Use the slope-intercept form to find b:
y=mx+b
-5=2·(-4)+b
8-5=b
3=b

Then y=2x+3

 Find the equation of the line that goes through these two points P(1,7) and Q(-1,9) Solution: y= x+