Question 455145
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find the slope of a line perpendicular to the line that passes through (3,9) and (7,15)
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        In the post by @mananth, there are many unnecessary calculations and many unnecessary words

        and reasoning.  His final answer  -0.67  for the slope of a perpendicular line is incorrect.


        I came to make a job in a way as it  SHOULD  be done.



<pre>
The slope of the line passing through the given points is

    m1 = {{{(y[2]-y[1])/(x[2]-x[1])}}} = {{{(15-9)/(7-3)}}} = {{{6/4}}} = {{{3/2}}}.


The slope of a perpendicular line is

    {{{m[2]}}} = -{{{1/m[1]}}} = {{{-2/3}}}.    <U>ANSWER</U>
</pre>

Solved.


No more calculations are needed. No more words and no more reasoning are needed.