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MTH 102 MTH 102 Past Questions Objective Question

Question

Find dy/dx if 3x2y + xy2 = 5.
Options
A <i>dy/dx = (y<sup>2</sup> + 6xy) / (3x<sup>2</sup> + 2xy)</i>
B <i>dy/dx = -(y<sup>2</sup> + 6xy) / (3x<sup>2</sup> + 2xy)</i>
Correct Answer
C <i>dy/dx = -(y<sup>2</sup> + 6xy) / (3x<sup>2</sup> - 2xy)</i>
D <i>dy/dx = (y<sup>2</sup> - 6xy) / (3x<sup>2</sup> - 2xy)</i>
Correct Answer

Option B is the correct answer.

Detailed Explanation

We need to use implicit differentiation with respect to x.Differentiate each term with respect to x, remembering that y is a function of x:d/dx(3x2y) + d/dx(xy2) = d/dx(5)Using the product rule for the first two terms:(d/dx(3x2) · y + 3x2 · dy/dx) + (d/dx(x) · y2 + x · d/dx(y2)) = 0(6xy + 3x2 dy/dx) + (1 · y2 + x · 2y dy/dx) = 06xy + 3x2 dy/dx + y2 + 2xy dy/dx = 0Group terms containing dy/dx:(3x2 + 2xy) dy/dx = -6xy - y2Factor out dy/dx and solve:dy/dx = -(y2 + 6xy) / (3x2 + 2xy).

Hint

Apply implicit differentiation, remembering the product rule and chain rule for terms involving y.

Question Info