Let the centre of the circle x2+y2+2gx+2fy+25=0 be in the first quadrant and lie on the line 2x-y=4. Let the area of an equilateral triangle inscribed in the circle be 27 3. Then the square of the length of the chord of the circle on the line x=1 is .
Answer
80
Solution
[figure]
Centre C(-g, -f)=(h, k) lies on 2x-y=4 k=2h-4
r2=g2+f2-25=h2+k2-25
Equilateral triangle inscribed in a circle of radius r : side = 3r
area = 34 (3r2 )= 3 34r2=27 3 r2=36
h2+(2h-4)2-25=36 5h2-16h-45=0
(h-5)(5h+9)=0
First quadrant h=5, k=6; C(5, 6), r=6
Distance of C from the line x=1 : CM=4
Half chord AM= r2-CM2= 36-16= 20
AB2= (2 20 )2=80
Answer: 80