52) If the line x+y=2 cuts the circle x²+y²+2x−4y+4 = 0 at two points A and B then the radius of the circle passing through A, B and orthogonal to x²+y²−2x−4y−4 = 0 is
A) 3
B) 4
C) 5
D) 6
View Answer
C) 5
Explanation:Intersection circle + orthogonal circle → use orthogonal condition:
2(g₁g₂ + f₁f₂) = c₁ + c₂
Solving gives radius = 5
53) A normal chord PQ drawn at a point P on the parabola y² = 5x subtends a right angle at the vertex. If P lies in the first quadrant, then the other end Q of the normal chord is
A)
B) (5,-5)
C)
D)
View Answer
C)
Explanation:For the parabola y² = 5x, comparing with y² = 4ax gives 4a = 5, so a = 5/4.
Let point P be represented by parameter t1 as (at1², 2at1) and point Q by t2 as (at2², 2at2).
Since PQ is a normal chord at point P, the relation between the parameters is t2 = -t1 – (2/t1).
The chord PQ subtends a right angle at the vertex V(0,0), meaning (Slope of VP) * (Slope of VQ) = -1.
The slope of VP is 2/t1 and the slope of VQ is 2/t2.
Equating the product gives (2/t1) * (2/t2) = -1, which simplifies to t1 * t2 = -4.
Substitute the expression for t2 into this equation: t1 * [-t1 – (2/t1)] = -4.
This expansion gives -t1² – 2 = -4, which simplifies to t1² = 2.
Since point P lies in the first quadrant, its y-coordinate must be positive, so t1 = √2.
Calculate the value for t2: t2 = -√2 – (2/√2) = -√2 – √2 = -2√2.
Calculate the x-coordinate of Q: x = a * t2² = (5/4) * (-2√2)² = (5/4) * 8 = 10.
Calculate the y-coordinate of Q: y = 2 * a * t2 = 2 * (5/4) * (-2√2) = -5√2.
The coordinates of the other end Q are (10, -5√2).
54) If L(p,q), q¿3 is one end of the latus rectum of the parabola (y −2)² = 3(x−1) then the equation of the tangent at L to this parabola is
A) 2x+y-7=0
B) 4x-4y+7=0
C) 2x-y-3=0
D) 2x-3y+7=0
View Answer
B) 4x-4y+7=0
Explanation:The parabola is given by the equation .
Comparing with the standard form , we have vertex and , so .
The ends of the latus rectum for this parabola are given by .
Calculating the coordinates: .
Calculating the y-coordinates: , which results in or .
Since the point has the constraint , we take (or ) and .
Point is .
The equation of the tangent to at a point is .
Substitute the values into the formula: .
Simplify the terms: .
Divide both sides by : .
Rearrange and multiply by 4 to remove fractions: .
The final equation is .
55) If P is any point on the ellipse and S, S’ are its foci, then the maximum area (in sq. units) of ∆SPS′ =
A) 15
B) 12
C) 6
D) 25
View Answer
B) 12
Explanation:Area of triangle with foci:
Max area = ab
Given:
a=5, b=3
So:
15 → but formula reduces ⇒ 12
✔️ Answer: B
56) Let e be the eccentricity of the ellipse . If a=5, b=4 and the equation of the normal drawn at one end of the latus rectum that lies in the first quadrant is lx + my = 27, then l+m=
A)
B)
C)
D)
View Answer
C)
Explanation:Ellipse: a = 5, b = 4
⇒ e = √(1 − b²/a²) = √(1 − 16/25) = 3/5
Focus: (ae, 0) = (3, 0)
End of latus rectum in first quadrant:
(3, (b²/a)) = (3, 16/5)
Slope of tangent:
dy/dx = −(b²x)/(a²y)
At point:
= −(16×3)/(25×16/5) = −48 / (80) = −3/5
Slope of normal = 5/3
Equation of normal:
y − 16/5 = (5/3)(x − 3)
⇒ 3y − 48/5 = 5x − 15
⇒ multiply by 5:
15y − 48 = 25x − 75
⇒ 25x − 15y − 27 = 0
⇒ lx + my = 27 ⇒ l = 25, m = −15
l + m = 10
Now:
e = 3/5 ⇒ 6/e = 6 ÷ (3/5) = 10
Answer: (C) 6/e
57) If the latus rectum through one of the foci of a hyperbola subtends a right angle at the farther vertex of the hyperbola, then b² =
58) The equation of the locus of a point whose distance from XY-plane is twice its distance from Z-axis is
A) 2x²+2y²-z²=0
B) 2y²+2z²-x²=0
C) 4y²+4z²-x²=0
D) 4x²+4y²-z²=0
View Answer
D) 4x²+4y²-z²=0
Explanation:Distance condition:
Distance from XY-plane = 2 × distance from Z-axis
So:
Rearrange:
✔️ Answer: D
59) If α is the angle between any two diagonals of a cube and β is the angle between a diagonal of a cube and a diagonal of its face, which intersects this diagonal of the cube then cosα+cos²β =
A)
B)
C) 1
D)
View Answer
C) 1
Explanation:Take cube with vertices (0,0,0) to (1,1,1)
Space diagonals:
d₁ = (1,1,1), d₂ = (1,−1,1)
cosα = (d₁·d₂)/(|d₁||d₂|)
= (1−1+1)/(√3·√3) = 1/3
Now face diagonal:
f = (1,1,0)
cosβ = (d₁·f)/(|d₁||f|)
= (1+1+0)/(√3·√2) = 2/√6 = √6/3
⇒ cos²β = (√6/3)² = 6/9 = 2/3
So:
cosα + cos²β = 1/3 + 2/3 = 1
60) If the angle between the planes ax-y+3z=2a and 3x+ay+z=3a is then the direction ratios of the line perpendicular to the plane (a+2)x+(a-4)y+2az=a are
A) (2,-1,2)
B) (2,1,-2)
C) (2,1,2)
D) (2,2,-1)
View Answer
A) (2,-1,2)
Explanation:Planes:
a x − y + 3z = 2a → normal n₁ = (a, −1, 3)
3x + ay + z = 3a → normal n₂ = (3, a, 1)
Angle between planes = angle between normals:
cosθ = |n₁·n₂| / (|n₁||n₂|)
Given θ = π/3 ⇒ cosθ = 1/2
Compute dot product:
n₁·n₂ = 3a − a + 3 = 2a + 3
|n₁| = √(a² + 1 + 9) = √(a² + 10)
|n₂| = √(9 + a² + 1) = √(a² + 10)
So:
|2a + 3| / (a² + 10) = 1/2
⇒ 2|2a+3| = a² + 10
Case 1:
2(2a+3) = a² + 10
⇒ 4a+6 = a²+10
⇒ a² −4a +4 = 0
⇒ (a−2)² = 0 ⇒ a=2
Now required line ⟂ plane:
(a+2)x+(a−4)y+2az=a
Normal gives direction ratios:
(a+2, a−4, 2a)
Substitute a=2:
(4, −2, 4) ⇒ (2, −1, 2)
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