# on the grid below,choose three non collinear points a,b and c. connect ab with a rurer.a)find the equation of line ab in slope intercept form.b)find the equation of the line passing through c and...

on the grid below,choose three non collinear points a,b and c. connect ab with a rurer.a)find the equation of line ab in slope intercept form.

b)find the equation of the line passing through c and perpendicular to AB.

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First knowing that the slope intercept form is

`y = mx+b` where m is the slope (rise over run) and b is the y intercept (x=0).

Pick points a and b that will be easy to use, such as 0, 2 and 6, 5.

The slope is 3/6 and the y intercept is 2 so the first equation is

`y = (1/2)x + 2`

Point c must be off of the line in question such as 0,0

Using the point slope formula and the fact that the product of the slopes of perpendicular lines is -1, you can find the other equation.

The slope must be the opposite of the reciprocal of the first slope in order to get a product of -1 so the second slope is `-2` .

The point slope formula is

`y-y' = m(x-x')`

Substituting the point c for x' and y' you get

`y-0 = (-2)(x-0)` or ` <strong>y =-2x</strong> `

You can see now why I chose 0.0.  You can choose any other point that is not on the first line and solve for y, it just takes more steps.