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MTH 102 MTH 102 Past Questions Objective Question

Question

Differentiate the implicit functions x2 siny - e2y cosx = 3x2 + 2x - 5 with respect to x.
Options
A dy/dx = (6x - 2xsiny - sinxe<sup>2y</sup> + 2) / (x<sup>2</sup>cosy + 2cosxe<sup>2y</sup>)
B dy/dx = (6x + 2xsiny - sinxe<sup>2y</sup> + 2) / (x<sup>2</sup>cosy - 2cosxe<sup>2y</sup>)
C dy/dx = (6x - 2xsiny - sinxe<sup>2y</sup> + 2) / (x<sup>2</sup>cosy - 2cosxe<sup>2y</sup>)
Correct Answer
D dy/dx = (-6x - 2xsiny - sinxe<sup>2y</sup> - 2) / (x<sup>2</sup>cosy - 2cosxe<sup>2y</sup>)
Correct Answer

Option C is the correct answer.

Detailed Explanation

Differentiate each term with respect to x using the product rule and chain rule:1. d/dx(x2 siny) = 2x siny + x2 cos y (dy/dx)2. d/dx(e2y cosx) = (d/dx(e2y)) cosx + e2y (d/dx(cosx)) = (2e2y dy/dx) cosx + e2y (-sinx) = 2e2y cosx (dy/dx) - e2y sinx3. d/dx(3x2 + 2x - 5) = 6x + 2Substitute these back into the original differentiated equation:(2x siny + x2 cos y dy/dx) - (2e2y cosx dy/dx - e2y sinx) = 6x + 22x siny + x2 cos y dy/dx - 2e2y cosx dy/dx + e2y sinx = 6x + 2Group terms with dy/dx:dy/dx (x2 cos y - 2e2y cosx) = 6x + 2 - 2x siny - e2y sinxSolve for dy/dx:dy/dx = (6x + 2 - 2x siny - e2y sinx) / (x2 cos y - 2e2y cosx).Rearranging the numerator terms: (6x - 2xsiny - sinxe2y + 2).This exactly matches option C.

Hint

Be careful with the signs when differentiating terms, especially when subtracting a product that itself contains a negative derivative. Remember to group all dy/dx terms to one side.

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