Class CBSE Class 12 Mathematics Derivatives Q #1389
KNOWLEDGE BASED
UNDERSTAND
3 Marks 2025 AISSCE(Board Exam) SA
If $x\sqrt{1+y}+y\sqrt{1+x}=0$, $-1

AI Tutor Explanation

Powered by Gemini

Detailed Solution

Step 1: Isolate one term

Given the equation $x\sqrt{1+y}+y\sqrt{1+x}=0$, we isolate one of the terms. Let's isolate $x\sqrt{1+y}$:

Step 2: Rewrite the equation

Rewrite the equation as: $x\sqrt{1+y} = -y\sqrt{1+x}$

Step 3: Square both sides

Square both sides of the equation to eliminate the square roots: $(x\sqrt{1+y})^2 = (-y\sqrt{1+x})^2$ $x^2(1+y) = y^2(1+x)$

Step 4: Expand the equation

Expand both sides of the equation: $x^2 + x^2y = y^2 + y^2x$

Step 5: Rearrange the terms

Rearrange the terms to bring all terms to one side: $x^2 - y^2 + x^2y - y^2x = 0$

Step 6: Factor the equation

Factor the difference of squares and factor out $xy$: $(x-y)(x+y) + xy(x-y) = 0$

Step 7: Factor out (x-y)

Factor out the common term $(x-y)$: $(x-y)(x+y+xy) = 0$

Step 8: Consider the two possible solutions

This gives us two possible solutions: 1. $x-y = 0 \Rightarrow x = y$ 2. $x+y+xy = 0$

Step 9: Analyze the first solution (x=y)

If $x=y$, substituting into the original equation gives: $x\sqrt{1+x} + x\sqrt{1+x} = 0$ $2x\sqrt{1+x} = 0$ This implies $x=0$ or $x=-1$. Since $x > -1$, both are valid solutions. However, we are looking for a general expression for $\frac{dy}{dx}$.

Step 10: Analyze the second solution (x+y+xy=0)

Consider the second solution $x+y+xy = 0$. We want to find $\frac{dy}{dx}$. Rewrite the equation as $y(1+x) = -x$, so $y = \frac{-x}{1+x}$.

Step 11: Differentiate y with respect to x

Differentiate $y$ with respect to $x$ using the quotient rule: $\frac{dy}{dx} = \frac{d}{dx} \left(\frac{-x}{1+x}\right) = \frac{(-1)(1+x) - (-x)(1)}{(1+x)^2} = \frac{-1-x+x}{(1+x)^2} = \frac{-1}{(1+x)^2}$

Step 12: State the final answer

Therefore, $\frac{dy}{dx} = -\frac{1}{(1+x)^2}$.

Final Answer: $-\frac{1}{(1+x)^2}$

AI generated content. Review strictly for academic accuracy.

Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the given equation, algebraic manipulation, and differentiation to arrive at the solution.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding of implicit functions, algebraic manipulation, and differentiation rules (quotient rule). It's not just recalling facts but applying concepts.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's understanding of implicit differentiation, which is a standard topic in the syllabus.