The equation of the normal at (4,8) is y=−x+12 so, considerthe diagram,
The X-axis is cut at (12,0) So, the equation of chord passing through (12,0) and perpendicular to normal is y=x−12 Substitute the value of y in the equation y=16x then, (12−x)2‌‌=16x 144−24x+x2‌‌=16x x2−40x+144‌‌=0 (x−36)(x−4)‌‌=0 Simplify the above, x=4,36 This implies, y‌‌=4−12 ‌‌=−8 And, y‌‌=36−12 ‌‌=24 The length of chord is given by, √(36−4)2+(24+8)2‌‌=√322+322 ‌‌=32√2