JEE 2023 — Mathematics PYQ
JEE | Mathematics | 2023The slope of tangent at any point (x,y) on a curve y=y(x) is \frac{x^2 + y^2}{2xy}, x > 0 . If y(2)=0, then a value of y(8) is:
Choose the correct answer:
- A.
43
(Correct Answer) - B.
−42
43
Explanation
Given that, slope of tangent at any point is 2xyx2+y2
⇒dxdy=2xyx2+y2
which is a homogeneous differential eqn., so putting y=vx and dxdy=v+xdxdv, we get
v+xdxdv=2x×vxx2+v2x2=2v1+v2
xdxdv=2v1+v2−v=2v1+v2−2v2
⇒xdxdv=2v1−v2
or ∫1−v22vdv=∫xdx
−log(1−v2)=logx+logC
or 1−v21=Cx
or x2−y2x2=Cx⇒x=C(x2−y2)
But, it is given that y(2)=0
⇒2=C(4−0)⇒C=21
So,
x=21(x2−y2) or 2x=x2−y2
or y=x2−2x
Putting x=8
y(8)=82−2×8=64−16=48⇒y(8)=43
Explanation
Given that, slope of tangent at any point is 2xyx2+y2
⇒dxdy=2xyx2+y2
which is a homogeneous differential eqn., so putting y=vx and dxdy=v+xdxdv, we get
v+xdxdv=2x×vxx2+v2x2=2v1+v2
xdxdv=2v1+v2−v=2v1+v2−2v2
⇒xdxdv=2v1−v2
or ∫1−v22vdv=∫xdx
−log(1−v2)=logx+logC
or 1−v21=Cx
or x2−y2x2=Cx⇒x=C(x2−y2)
But, it is given that y(2)=0
⇒2=C(4−0)⇒C=21
So,
x=21(x2−y2) or 2x=x2−y2
or y=x2−2x
Putting x=8
y(8)=82−2×8=64−16=48⇒y(8)=43

