The axis of a parabola is the line y = x and its vertex and focus are in the first quadrant at distances sqrt2 and 2sqrt2 units from the origin, respectively. If the point (1, k) lies on the parabola, then a possible value of k is:

Solution & Explanation

### Related Formula For any point P on a parabola, its distance to the focus S equals its perpendicular distance to the directrix line M: PS = PM ### Core Logic The axis line is y = x. The vertex lies along this line at a distance of sqrt2 from the origin. Since it's in the first quadrant, its coordinates are (1,1). The focus also lies along y=x at a distance of 2sqrt2 from the origin, which gives coordinates (2,2). ### Step 1: Finding the Equation of the Directrix The distance from the vertex to the focus is a = sqrt(2-1)^2 + (2-1)^2 = sqrt2. The directrix is perpendicular to the axis line y = x (slope = 1), so the slope of the directrix is -1. The directrix is located at a distance a = sqrt2 behind the vertex, which brings it exactly to the origin (0,0). Therefore, the equation of the directrix line is: y - 0 = -1(x - 0) implies x + y = 0
Parabola diagram for Q57 - JEE Main 2025 Evening
Parabola diagram for Q57 - JEE Main 2025 Evening
### Step 2: Utilizing the Focus-Directrix Property Let the point P(1,k) lie on the parabola. Applying PS = PM: sqrt(1 - 2)^2 + (k - 2)^2 = frac|1 + k|sqrt1^2 + 1^2 Squaring both sides: 1 + (k - 2)^2 = frac(1 + k)^22 2big(1 + k^2 - 4k + 4big) = 1 + k^2 + 2k 2k^2 - 8k + 10 = k^2 + 2k + 1 k^2 - 10k + 9 = 0 Factoring the quadratic equations: (k - 1)(k - 9) = 0 implies k = 1 text or k = 9 ### Pattern Recognition When a vertex and focus both sit perfectly on a symmetric line like y=x, notice that the foot of the directrix often lands on a clean coordinate intersection (like the origin here), heavily simplifying geometric distance 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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