Question:

The equation of the normal to the curve $y(1 + x^2) = 2 - x$ where the tangent crosses $x-axis$ is

Updated On: May 14, 2024
  • $5 x - y - 10 = 0$
  • $ x - 5y - 10 = 0$
  • $5 x + y + 10 = 0$
  • $ x + 5 y + 10 = 0$
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The Correct Option is A

Solution and Explanation

We have, $y\left(1+x^{2}\right)=2-x\dots$(i)
Put $y=0 \Rightarrow x=2 [\because$ tangent crosses $X$ -axis]
On differentiating E (i) w.r.t. $x$, we get
$\frac{d y}{d x}\left(1+x^{2}\right)+2 x y=-1$
$ \Rightarrow \frac{d y}{d x}=\frac{-1-2 x y}{1+x^{2}}$
$\therefore\left(\frac{d y}{d x}\right)_{(2,0)}=\frac{-1-0}{1+4}=\frac{-1}{5}$
So, the slope of normal is $5$ .
$\therefore$ Equation of the normal at $(2,0)$ is
$ y-0 =5(x-2) $
$\Rightarrow y =5 x-10 $
$\Rightarrow 5 x-y-10 =0$
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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