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MTH 102 MTH 102 Past Questions Objective Question

Question

Find $\frac{dy}{dx}$ if $3x^2 y + xy^2 = 5$.
Options
A $\frac{dy}{dx} = \frac{y^2 + 6xy}{3x^2 + 2xy}$
B $\frac{dy}{dx} = -\frac{y^2 + 6xy}{3x^2 + 2xy}$
Correct Answer
C $\frac{dy}{dx} = -\frac{y^2 + 6xy}{3x^2 - 2xy}$
D $\frac{dy}{dx} = \frac{y^2 - 6xy}{3x^2 - 2xy}$
Correct Answer

Option B is the correct answer.

Detailed Explanation

To find $\frac{dy}{dx}$ for the implicit function $3x^2 y + xy^2 = 5$, we differentiate each term with respect to $x$.$d/dx(3x^2 y) + d/dx(xy^2) = d/dx(5)$Using the product rule:$d/dx(3x^2 y) = (d/dx(3x^2))y + 3x^2(d/dx(y)) = 6xy + 3x^2 \frac{dy}{dx}$$d/dx(xy^2) = (d/dx(x))y^2 + x(d/dx(y^2)) = 1 \cdot y^2 + x(2y \frac{dy}{dx}) = y^2 + 2xy \frac{dy}{dx}$$d/dx(5) = 0$Substitute these back into the equation:$(6xy + 3x^2 \frac{dy}{dx}) + (y^2 + 2xy \frac{dy}{dx}) = 0$Group terms with $\frac{dy}{dx}$:$3x^2 \frac{dy}{dx} + 2xy \frac{dy}{dx} = -6xy - y^2$$\frac{dy}{dx} (3x^2 + 2xy) = -(6xy + y^2)$Solve for $\frac{dy}{dx}$:$\frac{dy}{dx} = -\frac{y^2 + 6xy}{3x^2 + 2xy}$

Hint

Remember to use the product rule for $3x^2y$ and $xy^2$. For terms involving $y$, apply the chain rule, resulting in a $\frac{dy}{dx}$ factor.

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