If A and B are the points of intersection of the circle x^2+y^2-8x=0 and the hyperbola fracx^29-fracy^24=1 and a point P moves on the line 2x-3y+4=0, then the centroid of Delta PAB lies on the line:

Solution & Explanation

### Related Formula Centroid (h, k) of a triangle with vertices (x_1,y_1), (x_2,y_2), (x_3,y_3): h = fracx_1 + x_2 + x_33, quad k = fracy_1 + y_2 + y_33 ### Core Logic Given equations: 1) Circle: y^2 = 8x - x^2 2) Hyperbola: 4x^2 - 9y^2 = 36 Substitute circle's y^2 into hyperbola equation: 4x^2 - 9(8x - x^2) = 36 implies 4x^2 - 72x + 9x^2 = 36 13x^2 - 72x - 36 = 0 implies (13x + 6)(x - 6) = 0 If x = -6/13, y^2 < 0 (rejected). Thus, x = 6. Substituting x = 6 into circle: y^2 = 8(6) - 6^2 = 48 - 36 = 12 implies y = pm sqrt12. The intersection points are A(6, sqrt12) and B(6, -sqrt12). ### Step 1: Relate Centroid coordinates to P Let point P have coordinates (alpha, beta). Since P lies on 2x - 3y + 4 = 0: 2alpha - 3beta + 4 = 0 implies beta = frac2alpha + 43 Let the centroid be (h, k): h = frac6 + 6 + alpha3 = frac12 + alpha3 implies alpha = 3h - 12 k = fracsqrt12 - sqrt12 + beta3 = fracbeta3 implies beta = 3k ### Step 2: Form the Locus Equation Substitute alpha and \beta into the line equation of P: 2(3h - 12) - 3(3k) + 4 = 0 6h - 24 - 9k + 4 = 0 6h - 9k = 20 Replacing (h, k) with general coordinates (x, y) gives the locus: 6x - 9y = 20 ### Pattern Recognition Notice how the y-coordinates of intersection points A and B are symmetric (\,pmsqrt12\,), meaning their sum is zero. This simplifies the expression for k instantly to just beta/3. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Mathematics: Coordinate Geometry Class 11 Mathematics: Conic Sections

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Q27 jee_main_2024_31_jan_morning Ellipse and Hyperbola Properties
Let the foci and length of the latus rectum of an ellipse fracx^2a^2 + fracy^2b^2 = 1, a > b be (pm 5, 0) and sqrt50, respectively. Then, the square of the eccentricity of the hyperbola fracx^2b^2 - fracy^2a^2 b^2 = 1 equals
Numerical Answer. Answer: 51 to 51

Solution

### Core Logic For the ellipse, foci are at (pm 5, 0) implies ae = 5. Latus rectum = frac2b^2a = sqrt50 = 5sqrt2 implies b^2 = frac5sqrt2a2. ### Step 1: Solve for a and b Using b^2 = a^2(1 - e^2): a^2 - (ae)^2 = b^2 implies a^2 - 25 = frac5sqrt2a2 2a^2 - 5sqrt2a - 50 = 0 2a^2 - 10sqrt2a + 5sqrt2a - 50 = 0 2a(a - 5sqrt2) + 5sqrt2(a - 5sqrt2) = 0 a = 5sqrt2 (since a > 0). Now, b^2 = frac5sqrt2(5sqrt2)2 = 25 implies b = 5. ### Step 2: Hyperbola Eccentricity The hyperbola is fracx^2b^2 - fracy^2a^2b^2 = 1. Here, semi-major axis A = b and semi-minor axis B = ab. Using eccentricity formula for hyperbola e_H^2 = 1 + fracB^2A^2: e_H^2 = 1 + fraca^2 b^2b^2 = 1 + a^2 Since a = 5sqrt2, a^2 = 50. e_H^2 = 1 + 50 = 51 ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Maths: Conic Sections

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