put 3x-9y=9 in slope intercept form then state y-intercept and slope of the line...find the line that is perpendicular to this line and passes thru the point(2,7)thank you for your help

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hala718's profile pic

hala718 | High School Teacher | (Level 1) Educator Emeritus

Posted on

3x -9y = 9

First we will rewrite the equation as a function of x.

==>  3x -9 = 9y

==> 9y = 3x -9

Now we will divide by 9.

==> y= (1/3) x - 1  ( Slope-intercept form)

==> y-intercept is (0, -1)

The slope is m= 1/3

==> Slope of perpendicular line is -3

Given the point (2,7) passes through the perpendicular line.

==> y-y1 = m (x-x1)

==> y -7 = -3 (x-2)

==> y= -3x +6 +7

==> y= -3x +13  ( equation of perpendicular line)

 

 

Wiggin42's profile pic

Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

Posted on

3x - 9y = 9

Slope intercept form is y = mx + b. To change what you have into slope intercept, just solve for y. 

x - 3y = 3 (Divide out the 3s)

3y = x - 3 (Isolate y term)

y = (1/3)x - 1 (solve for y)

We know the slope is 1/3. A line perpendicular to this one would have a slope of -3. We want that line to pass through (2,7). We have a point and a slope so lets put that into point-slope form and we're done!

 y - 7 = -3(x - 2)

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