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MTH 102 MTH 102 Past Questions Objective Question

Question

Find dy/dx if y = xtanx.
Options
A dy/dx = -x<sup>tanx</sup> ( (tanx)/x - sec<sup>2</sup>x ln x )
B dy/dx = -x<sup>tanx</sup> ( (tanx)/x + sec<sup>2</sup>x ln x )
C dy/dx = x<sup>tanx</sup> ( (tanx)/x - sec<sup>2</sup>x ln x )
D dy/dx = x<sup>tanx</sup> ( (tanx)/x + sec<sup>2</sup>x ln x )
Correct Answer
Correct Answer

Option D is the correct answer.

Detailed Explanation

To differentiate y = xtanx, use logarithmic differentiation.Take the natural logarithm of both sides: ln y = ln(xtanx) = tanx * ln x.Differentiate both sides with respect to x using the product rule on the right side:(1/y) dy/dx = (d/dx(tanx)) * ln x + tanx * (d/dx(ln x))(1/y) dy/dx = sec2x * ln x + tanx * (1/x).Now, solve for dy/dx:dy/dx = y * (sec2x * ln x + (tanx)/x).Substitute y = xtanx back into the equation:dy/dx = xtanx ( sec2x * ln x + (tanx)/x ).This matches option D.

Hint

When the variable appears in both the base and the exponent, use logarithmic differentiation (take ln of both sides).

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