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Let y2 = 16x be a given parabola and L be an extremity of its latus rectum in the first quadrant. If a chord is drawn through L with slope-1, then the length of this chord is: 

a
32
b
162
c
163
d
322

detailed solution

Correct option is D

Equation of the latus rectum is x = 4 and the coordinates of L are (4, 8). Equation of the chord through L with slope-1 is y−8=−(x−4) ⇒x+y=12Solving the equation of the chord and the parabola we get y2=16(12−y)⇒y=8 and -24So the coordinates of M the other end of the chord through L is (36, –24). and LM=(36−4)2+(−24−8)2=322

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