Maths-
General
Easy

Question

Straight line ellx + my + n = 0 touches parabola y2 = 4ax if elln = amk then k =

  1. 1    
  2. 2    
  3. 3    
  4. fraction numerator 3 over denominator 2 end fraction    

The correct answer is: 2


    To find the value of k.

    The x-coordinates of the points of intersection of the line lx+my+n=0 and parabola is

    open parentheses negative fraction numerator l x plus n over denominator n end fraction close parentheses squared equals 4 a x

l squared x squared plus 2 x left parenthesis ln minus 2 a m squared right parenthesis plus n squared equals 0

I f space t h e space l i n e space l x plus m y plus n equals 0 space t o u c h e s space t h e space p a r a b o l a comma space t h e n space t h i s space e q u a t i o n space h a s space e q u a l space r o o t s

4 left parenthesis ln minus 2 a m squared right parenthesis squared minus 4 l to the power of 2 end exponent n to the power of 2 end exponent equals 0

minus 4 a l m squared n plus 4 a squared m to the power of 4 equals 0

ln equals a m squared

    Therefore, the value of k is 2.

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