An Equation Of A Line Through The Point (1, 2) Whose Distance From The Point (3, 1) Has The Greatest Value Is

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Question

An equation of a line through the point (1, 2) whose distance from the point (3, 1) has the greatest value is

Solution

Correct option is

y = 2x 

Let the equation of the line through (1, 2) be y – 2 = m(x – 1)  

If P denotes the length of the perpendicular from (3, 1) on this line, then

                 

  

Then P2 is greatest if and only if s is greatest 

   

                          

   

                                                      

                                                      

So s is greatest for m = 2

and thus the equation of the required line is y = 2x

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