Engineering
Mathematics
Homogeneous Differential Equation
Question
Column - I Column - II
(A) Let S1 and S2 are two points on AB of a ΔABC with vertices A (– 2, 3), B (4, – 6) and C (1, 1). CS1 and CS2 divide the triangle into three parts of equal area. If the equation of the lines through the origin drawn parallel to CS1 and CS2 is y2 + λxy – μx2 = 0 then the value of  (λ + μ), is (P) 2
(B) If the area enclosed by the curves  x2 – y2 = 0 and  x2 + y – 2 = 0 is pq,where p and q are coprime then the value of  (p – q), is (Q) 4

(C) The curve that satisfies the differential equation dydx=x2+y22xy is a hyperbola  passing through (2, 1)  with eccentricity e. The value of  e4 is equal to

(R) 6
 (D) Let Limn→∞  ∑r=1nℓn(n2+r2)−2n ℓn nn=ℓn 2+π2−2 if Limn→∞  1n2m [(n2+12)m(n2+22)m................(n2+n2)m]1n=(a eπe2)m.then the value of  a, is (S) 7
  (T) 8
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Solution

(A) CS1 and CS2 divide the triangle into three of equal area so that S1 and S2 are points of trisection of AB. Thus S1 = (0, 0), S2 = (2, – 3). Equation of CS1 is y – x = 0. Slope of CS2 = – 4. The line through (0, 0) drawn parallel to CS2 is y + 4x = 0

Required equation is  y2 + 3xy – 4x2 = 0 ⇒ λ + μ = 3 + 4 = 7

(B) The required area is bounded by the lines y = ± x  and the parabola x2 = – (y – 2) having the vertex at (0, 2) and passing through (±1, 1). By symmetry about the y-axis,

Area=2 [12 + ∫122−y dy]=73≡pq

⇒ p – q = 7 – 3 = 4

(C) With y = xv, xv' = 1+v22v−v=1−v22v⇒2v dv1−v2=dxx

whose solution is x(1 – v2) = c. When x = 2, v = v=12  so   that  c=32.

The equation of the curve is x2 – y2 = 3x2⇒(x−32)2−y2=916.

This is a rectangular hyperbola with eccentricity 2 .

∴ e4 = 4 

(D) P=Limn→∞  [(n2+12)(n2+22).......(n2+n2)]m/nn2m

In P=Limn→∞  mn [∑r=1nℓn(n2+r2)−2m ℓn n]

In P=m  Limn→∞   [∑r=1nℓn(n2+r2)−2n ℓn nn]

In P=m  [ℓn 2+π2−2]

P=em [ln 2+π2−2]=em ln 2 · e−2m· emπ2

=2memπ2e2m=(2eπ/2)me2m=(2eπe2)m

⇒ a = 2