Let S be the focus of the hyperbola 3x2−5y2=1, on the positive x -axis. Let C be the circle with its centre at A(6,5) and passing through the point S . if O is the origin and SAB is a diameter of C then the square of the area of the triangle OSB is equal to
Answer: 40
Solution
Hyperbola 3x2−5y2=1: a2=3,b2=5,c2=a2+b2=8, so S=(22,0). Centre A=(6,5); since SAB is a diameter of the circle centred at A, A is the midpoint of SB: B=2A−S=(26−22,25). Area of △OSB with O at the origin and S on the x-axis: Area=21∣OS∣⋅(height of B)=21(22)(25)=210.