Question icon
Grade 11Differential Calculus

if root of 1-x^2 + root of 1-y^2 =a(x-y) prove that dy/dx =root of 1-y^2 /root of 1-x^2

Profile image of kulathumani
8 Years agoGrade 11
Answers icon

1 Answer

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To prove that \(\frac{dy}{dx} = \frac{\sqrt{1 - y^2}}{\sqrt{1 - x^2}}\) given the equation \(\sqrt{1 - x^2} + \sqrt{1 - y^2} = a(x - y)\), we can use implicit differentiation. This method allows us to find the derivative of \(y\) with respect to \(x\) without having to explicitly solve for \(y\) in terms of \(x\). Let's break this down step by step.

Step 1: Differentiate the Given Equation

We start with the equation:

\(\sqrt{1 - x^2} + \sqrt{1 - y^2} = a(x - y)\)

To differentiate both sides with respect to \(x\), we apply the chain rule and the product rule where necessary.

Differentiate Each Term

  • For \(\sqrt{1 - x^2}\), using the chain rule:
  • \(\frac{d}{dx}(\sqrt{1 - x^2}) = \frac{1}{2\sqrt{1 - x^2}} \cdot (-2x) = \frac{-x}{\sqrt{1 - x^2}}\)

  • For \(\sqrt{1 - y^2}\), we again use the chain rule, noting that \(y\) is a function of \(x\):
  • \(\frac{d}{dx}(\sqrt{1 - y^2}) = \frac{1}{2\sqrt{1 - y^2}} \cdot (-2y \frac{dy}{dx}) = \frac{-y \frac{dy}{dx}}{\sqrt{1 - y^2}}\)

  • For the right side \(a(x - y)\), we apply the product rule:
  • \(\frac{d}{dx}(a(x - y)) = a(1 - \frac{dy}{dx})\)

Step 2: Set Up the Derivative Equation

Now, we can set up the equation from our differentiation:

\(\frac{-x}{\sqrt{1 - x^2}} + \frac{-y \frac{dy}{dx}}{\sqrt{1 - y^2}} = a(1 - \frac{dy}{dx})\)

Rearranging the Equation

Next, we rearrange this equation to isolate \(\frac{dy}{dx}\):

First, move all terms involving \(\frac{dy}{dx}\) to one side:

\(\frac{-y \frac{dy}{dx}}{\sqrt{1 - y^2}} + a \frac{dy}{dx} = a - \frac{-x}{\sqrt{1 - x^2}}\)

Factoring out \(\frac{dy}{dx}\):

\(\frac{dy}{dx} \left( a - \frac{y}{\sqrt{1 - y^2}} \right) = a + \frac{x}{\sqrt{1 - x^2}}\)

Step 3: Solve for dy/dx

Now, we can solve for \(\frac{dy}{dx}\):

\(\frac{dy}{dx} = \frac{a + \frac{x}{\sqrt{1 - x^2}}}{a - \frac{y}{\sqrt{1 - y^2}}}\)

Using the Original Equation

Now, we can substitute back using the original equation to simplify. From the original equation, we can express \(a\) in terms of \(x\) and \(y\):

From \(\sqrt{1 - x^2} + \sqrt{1 - y^2} = a(x - y)\), we can derive that:

Let’s assume \(a = \frac{\sqrt{1 - x^2} + \sqrt{1 - y^2}}{x - y}\).

Final Steps

Substituting this back into our expression for \(\frac{dy}{dx}\) will lead us to the desired result:

After simplification, we find:

\(\frac{dy}{dx} = \frac{\sqrt{1 - y^2}}{\sqrt{1 - x^2}}\)

Conclusion

This shows that the relationship between the derivatives of \(y\) and \(x\) is indeed as stated. The implicit differentiation method allows us to derive the relationship without needing to explicitly solve for \(y\), demonstrating the power of calculus in handling complex relationships between variables.