COMEDK2014MathematicsApplication of Derivatives
The point on the circle x²+y²=2 at the abscissa and ordinate increase at the same ate is
Options
- A(-1,-1)
- B(1,-1)
- C(1,1)
- D(-1,4)
Correct answer
B. (1,-1)
Step-by-step solution
Given, equation of circle is x²+y²=2 ...(i) Taking derivative w.r.t. ' t ' on both sides. 2 x d x d t +2 y d y d t =0 x d x d t +y d y d t =0 If abscissa and ordinate increase at the same rate, we have d x d t = d y d t x d x d t +y d x d t =0 d x d t (x+y)=0 Since, x+y=0 x=-y ...(ii) Solving Eqs. (i) and (ii), we get x²+(-x)²=2 x= 1 For x=1, y=-1 and x=-1, y=1 Required point are (1,-1) and (-1,1) .