Join the Most Relevant JEE Main 2025 Test Series & get 99+ percentile! Join Now
Search any question & find its solution
Question: Answered & Verified by Expert
The point on the circle $x^{2}+y^{2}=2$ at the abscissa and ordinate increase at the same ate is
MathematicsApplication of DerivativesCOMEDKCOMEDK 2014
Options:
  • A $(-1,-1)$
  • B $(1,-1)$
  • C $(1,1)$
  • D $(-1,4)$
Solution:
1800 Upvotes Verified Answer
The correct answer is: $(1,-1)$
Given, equation of circle is
$$
x^{2}+y^{2}=2 \quad \text{...(i)}
$$
Taking derivative w.r.t. ' $t$ ' on both sides.
$$
2 x \frac{d x}{d t}+2 y \frac{d y}{d t}=0 \Rightarrow x \frac{d x}{d t}+y \frac{d y}{d t}=0
$$
If abscissa and ordinate increase at the same rate, we have
$$
\frac{d x}{d t}=\frac{d y}{d t}
$$
$$
x \frac{d x}{d t}+y \frac{d x}{d t}=0 \Rightarrow \frac{d x}{d t}(x+y)=0
$$
Since,
$$
\Rightarrow \quad x+y=0 \Rightarrow x=-y \quad \text{...(ii)}
$$
Solving Eqs. (i) and (ii), we get
$$
x^{2}+(-x)^{2}=2 \Rightarrow x=\pm 1
$$
For $x=1, y=-1$ and $x=-1, y=1$
Required point are $(1,-1)$ and $(-1,1)$.

Looking for more such questions to practice?

Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.