SOLUTION: I dont understand how to write an equation of the line that passes through (-2,1) and is perpindicular to y=1/2x+1.

Question 499869: I dont understand how to write an equation of the line that passes through (-2,1) and is perpindicular to y=1/2x+1.

Answer by oberobic(2304) (Show Source): You can put this solution on YOUR website!
y = 1/2x + 1 is an equation in y = mx + b form.
This form is known as "slope-intercept" because m is the slope and b is the y-intercept.
.
The slope of a line perpendicular to this line will have slope = inverse reciprocal.
The inverse reciprocal of 1/2 is -2.
.
So the line we're looking for is:
y = -2x + b
.
It will run from the upper left corner of the graph to the lower right corner.
The y value will be decreasing as the x value is increasing.
.
There are infinitely many lines with slope -2.
But only one line with slope = -2 will go through the point (-2,1).
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Notice that (-2,1) means that when x=-2, y=1.
.
We can plug that into the equation and find 'b'.
.
y = -2x + b
1 = -2(-2) + b
1 = 4 + b
subtract 4 from both sides
-3 = b
so
b = -3
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That means the equation you need to find is:
y = -2x -3
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The following graphs show the two lines.
.

.
Done.
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