Question 1137657
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The distance from D to the line containing E and F is the length of the line segment from D that is perpendicular to the line.<br>
This particular example is easily solved using equations of perpendicular lines.  I'll outline the process; you can fill in the details if you need.<br>
(1) From the coordinates of E and F, we can determine that the equation of the line E and F is y = x+2.
(2) The slope of the line containing E and F is 1; the slope of a line perpendicular to that line is -1.
(3) The line with slope -1 passing through D(4,-2) is y = -x+2.
(4) The intersection of y=x+2 and y=-x+2 is (0,2).
(5) The distance from (4,-2) to (0,2) is 4*sqrt(2).<br>
ANSWER: The distance from D to the line containing E and F is 4*sqrt(2).<br>
In general, there is a concise formula for finding the distance from a given point to a given line.<br>
If the equation of the line is in the form Ax+By+C=0, and the coordinates of the point are (a,b), then the distance from the point to the line is<br>
{{{abs((Aa+Bb+C)/sqrt(A^2+B^2))}}}<br>
In this example, after finding the equation y=x+2 for the line containing E and F, put it in the required form:<br>
{{{x-y+2=0}}}<br>
and plug the numbers into the formula (A=1, B=-1, C=2; (a,b) = (4,-2):<br>
{{{abs((4+2+2)/sqrt(1+1)) = 8/sqrt(2) = 4*sqrt(2)}}}