Let C_1 be the curve obtained by the solution of differential equation 2xy dy dx=y^2-x^2,x>0. Let the curve C_2 be the solution of 2xy x^2-y^2= dy…
JEE Main 2021 — Mathematics Calculus
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Let C1 be the curve obtained by the solution of differential equation 2xydxdy=y2−x2,x>0. Let the curve C2 be the solution of x2−y22xy=dxdy. If both the curves pass through (1,1), then the area (in sq. units) enclosed by the curves C1 and C2 is equal to :
Official previous-year question
Held on 16 Mar 2021 · Verified 6 Jul 2026.
Options
A
π−1
B
2π−1
C
π+1
D
4π+1
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Solution
dxdy=2xyy2−x2,x∈(0,∞)
put y=vx
xdxdv+v=2vv2−1
v2+12vdv=−xdx
Integrate,
ln(v2+1)=−lnx+C
ln(x2y2+1)=−lnx+C
put x=1,y=1,C=ln2
ln(x2y2+1)=−lnx+ln2
⇒x2+y2−2x=0 (Curve C1)
Similarly,
dxdy=x2−y22xy
Put y=vx
x2+y2−2y=0
Required area =2∫01(2x−x2−x)dx=2π−1 sq. units
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