KCET · Maths · Differential Equations
The family of curves whose \(x\) and \(y\) intercepts of a tangent at any point are respectively double the \(x\) and \(y\) coordinates of that point is
- A \(x y=C\)
- B \(x^2+y^2=C\)
- C \(x^2-y^2=C\)
- D \(\frac{y}{x}=C\)
Answer & Solution
Correct Answer
(A) \(x y=C\)
Step-by-step Solution
Detailed explanation
Let the point on the curve be \((h, k)\).
According to the question, the equation of the tangent will be
\(\Rightarrow \quad \frac{x}{2 h}+\frac{y}{2 k}=1\)
\(\Rightarrow \quad \frac{y}{2 k}=1-\frac{y}{2 h}\)
\(\Rightarrow \quad y=-\left(\frac{2 k}{2 h}\right) x+2 k\)
So, the slope of tangent will be \(\left(-\frac{k}{h}\right)\).
Now, \(\quad \frac{d y}{d x}=-\frac{h}{k}=-\frac{y}{x}\)
\(\Rightarrow \quad \frac{d y}{y}=-\frac{d x}{x}\)
On integrating both sides, we get
\(\int \frac{d y}{d y}=-\int \frac{d x}{x}\)
\(\Rightarrow \quad \ln y=-\ln x+\ln C\)
\(\Rightarrow \quad \ln y=\ln \frac{C}{x}\)
\(\Rightarrow \quad y=\frac{C}{x}\)
\(\therefore \quad x y=C\)
According to the question, the equation of the tangent will be
\(\Rightarrow \quad \frac{x}{2 h}+\frac{y}{2 k}=1\)
\(\Rightarrow \quad \frac{y}{2 k}=1-\frac{y}{2 h}\)
\(\Rightarrow \quad y=-\left(\frac{2 k}{2 h}\right) x+2 k\)
So, the slope of tangent will be \(\left(-\frac{k}{h}\right)\).
Now, \(\quad \frac{d y}{d x}=-\frac{h}{k}=-\frac{y}{x}\)
\(\Rightarrow \quad \frac{d y}{y}=-\frac{d x}{x}\)
On integrating both sides, we get
\(\int \frac{d y}{d y}=-\int \frac{d x}{x}\)
\(\Rightarrow \quad \ln y=-\ln x+\ln C\)
\(\Rightarrow \quad \ln y=\ln \frac{C}{x}\)
\(\Rightarrow \quad y=\frac{C}{x}\)
\(\therefore \quad x y=C\)
See the Complete Solution
Get step-by-step explanations for this and 2.5 Lakh+ more JEE, NEET & CET questions.
- Unlock all solutions
- Practice the full chapter
- Track accuracy across PYQs
4.8 rated on Google Play · 14,000+ reviews
More questions from Maths
- The points \((11,9),(2,1)\) and \((2,-1)\) are the mid-points of the sides of the triangle. Then, the centroid isKCET 2012 Medium
- The integrating factor of the differential equation \( x \cdot \frac{d y}{d x}+2 y=x^{2} \) is \( (x \neq 0) \)KCET 2017 Medium
- The value of \(\cos \left(\sin ^{-1} \frac{\pi}{3}+\cos ^{-1} \frac{\pi}{3}\right)\) isKCET 2020 Medium
- The value of \(\left|\begin{array}{lll}x & p & q \\ p & x & q \\ p & q & x\end{array}\right|\) isKCET 2007 Medium
- The equation of the curve passing through the point \( (1,1) \) such that the slope of the tangent at
any point \( (x, y) \) is equal to the product of its co-ordinates isKCET 2019 Medium - The rate of change of area of a circle with respect to its radius \( r=2 \mathrm{cms} \) isKCET 2016 Easy
More PYQs from KCET
- The size of the image of an object, which is at infinity, as formed by a convex lens of focal length \(30 \mathrm{~cm}\) is \(2 \mathrm{~cm}\). If a concave lens of focal length \(20 \mathrm{~cm}\) is placed between the convex lens and the image at a distance of \(26 \mathrm{~cm}\) from the lens, the new size of the image isKCET 2021 Easy
- The value of \( \tan \left(1^{\circ}\right)+\tan \left(89^{\circ}\right) \) isKCET 2015 Medium
- IUPAC name of \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl}\) isKCET 2009 Easy
- Which of the following possess net dipole moment?KCET 2019 Easy
- The correct set of four quantum numbers for outermost electron of potassium \((Z=19)\) isKCET 2009 Easy
- If the line \(6 x-7 y+8+\lambda(3 x-y+5)=0\) is parallel to \(y\)-axis, then \(\lambda\) is equal toKCET 2013 Medium