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Question

Column-I Column-II
(I) The curve C which passes through (1,1) and has differential equation as (2x2y2y4)dx+(2x3+3xy3)dy=0 is given by αln|x|+βln|y|+y3x2=γ, then (α+β+γ) equals- (P) 1
(II) A curve y=f(x) passes through (2,0) and slope of tangent at any point P(x,y) on it equals (x+1)2+(y3)(x+1), then f(3) is- (Q) 3
(III) Let f:R+R satisfies the functional equation f(xy)=exyyx(eyf(x)+exf(y)) for all x,yR+. If f(1)=e, then ln(ln(f(e))) equals- (R) 5
(IV) A curve y=f(x) passing through the point (12,14) satisfies the differential equation xydydx=3x2y2yx2 is a conic whose length of latus rectum is- (S) 2
(T) 4

Which of the following is only correct combination?

A
(I)(P)
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B
(II)(Q)
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C
(III)(R)
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D
(IV)(T)
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Solution

The correct option is B (II)(Q)
(I)
2x2ydx2y4dx+2x3dy+3xy3dy=0
Dividing both side by x3y we have
2dxx2y3x3dx+2dyy+3y2x2dy=02d(lnx)+2d(lny)+d(y3x2)=02ln|x|+2ln|y|+y3x2=C
Putting (1,1), C=1
So, α+β+γ=5

(II)
dydx=(x+1)2+(y3)(x+1)dydx+(11+x)y=x2+2x2x+1I.F=e(11+x)dx=(11+x)y.(11+x)=(x+1)23(1+x)2dx+Cy1+x=x+3x+1+C
Putting(2,0), C=3
y1+x=x+3x+13y(3)=3

(III)
Differentiating w.r.t x and taking y as constant
f(xy)y=exyyx(y1)(eyf(x)+exf(y))+exyyx(eyf(x)+exf(y))
Now, at x=1,y=1f(1)=e
which gives, f(1)=0
For, x=1, we have
f(y)y=e1(y1)(ef(y))+e1(eey+ef(y))yxf(x)f(x)=exxexf(x)exf(x)e2x=1xddx(f(x)ex)=1xf(x)=exlnx
ln(ln(f(e)))=1

(IV)
2xydyx3dy=3x2ydxy2dx2xydy+y2dx=3x2ydx+x3dyd(xy2)=d(xy3)+Cxy2=xy3+CAt x=12, y=14C=0y=x2Length of Latus Rectum=1

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