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find points on the circle x2+y2=a2 tangent are drawn to hyperbola x2-y2=a2 find locus of middle point of chord of contact

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The equation of circle is :x2+y2=a2 ...1Any point on the circle is Pa cos θ, a sin θ.Equation of chord of contact of the tangents from P to hyperbola x2-y2 = a2 is x cos θ - y sin θ = a ...2Let Mx1,y1 be the mid point of the chord of contact 2.Then its equation is :xx1 - yy1 = x12-y12 ....3Equations 2 and 3 represent chord of contact.Comparing the coefficients of like terms in 2 and 3, we getcos θx1 = sin θy1 = ax12-y12sin θ = ay1x12-y12 and cos θ = ax1x12-y12Now, sin2θ + cos2θ = 1a2y12+a2x12x12-y122 = 1x12-y122 = a2x12+y12So, locus of mid point M is,x2-y22 = a2x2+y2

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