Question:

The equation of the tangent to the conic $x^{2}-y^{2}-8x+2y+11=0$ at $(2,1)$ is

Updated On: Apr 26, 2024
  • $x + 2 = 0$
  • $2 x +1 = 0$
  • $x + y +1 = 0$
  • $x - 2 = 0$
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The Correct Option is D

Solution and Explanation

Equation of the tangent at $\left(x_{1}, y_{1}\right)$ is
$xx_{1}-yy_{1}-4\left(x+x_{1}\right)+\left(y+y_{1}\right)+11=0$
Put $x_{1}=2$ and $ y_{1}=1$, we get
$2x - y - 4\left(x + 2\right)+ \left(y + 1\right)+ 11 = 0$
$\Rightarrow - 2x - 8 + 12= 0$
$\Rightarrow x-2=0$
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Concepts Used:

Application of Derivatives

Various Applications of Derivatives-

Rate of Change of Quantities:

If some other quantity ‘y’ causes some change in a quantity of surely ‘x’, in view of the fact that an equation of the form y = f(x) gets consistently pleased, i.e, ‘y’ is a function of ‘x’ then the rate of change of ‘y’ related to ‘x’ is to be given by 

\(\frac{\triangle y}{\triangle x}=\frac{y_2-y_1}{x_2-x_1}\)

This is also known to be as the Average Rate of Change.

Increasing and Decreasing Function:

Consider y = f(x) be a differentiable function (whose derivative exists at all points in the domain) in an interval x = (a,b).

  • If for any two points x1 and x2 in the interval x such a manner that x1 < x2, there holds an inequality f(x1) ≤ f(x2); then the function f(x) is known as increasing in this interval.
  • Likewise, if for any two points x1 and x2 in the interval x such a manner that x1 < x2, there holds an inequality f(x1) ≥ f(x2); then the function f(x) is known as decreasing in this interval.
  • The functions are commonly known as strictly increasing or decreasing functions, given the inequalities are strict: f(x1) < f(x2) for strictly increasing and f(x1) > f(x2) for strictly decreasing.

Read More: Application of Derivatives