Let P(alpha, beta) be a point on the parabola y^2 = 4x. If P also lies on the chord of the parabola x^2 = 8y whose mid point is left(1, frac54right), then (alpha - 28)(beta - 8) is equal to

Numerical Answer Type:
Enter a numerical value Answer: 192 to 192 +4 marks

Solution & Explanation

### Related Formula Equation of chord with given midpoint (x_1, y_1) is T = S_1. ### Core Logic For the parabola x^2 = 8y, the equation of the chord with midpoint left(1, frac54right) is: x(1) - 4left(y + frac54right) = 1^2 - 8left(frac54right) x - 4y - 5 = 1 - 10 = -9 x - 4y + 4 = 0 quad dots (i) ### Step 1: Point Intersection with Paraboloid Curve Since P(alpha, beta) lies on this chord and also on y^2 = 4x: 1) alpha - 4beta + 4 = 0 implies alpha = 4beta - 4 2) beta^2 = 4alpha Substituting alpha into the equation: beta^2 = 4(4beta - 4) implies beta^2 - 16beta + 16 = 0 ### Step 2: Calculating the Target Value We need to find the value of (alpha - 28)(beta - 8). Substitute alpha = 4beta - 4 into this targeted expression: textValue = (4beta - 4 - 28)(beta - 8) = (4beta - 32)(beta - 8) = 4(beta - 8)(beta - 8) = 4(beta^2 - 16beta + 64) From the quadratic step, we know beta^2 - 16beta = -16. Substituting this: textValue = 4(-16 + 64) = 4(48) = 192 ### Pattern Recognition Do not solve for ugly root combinations explicitly if the target expression can be algebraically mapped back to the defining quadratic equations. This prevents unnecessary fractional math steps. ### Evaluation Rubric / Model Answer null ### Chapter Mix 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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