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MTH 102 MTH 102 Past Questions Objective Question

Question

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

Option D is the correct answer.

Detailed Explanation

This requires logarithmic differentiation:Given y = xtan xTake the natural logarithm of both sides: ln(y) = ln(xtan x)Using logarithm properties: ln(y) = tan x * ln xNow, differentiate both sides with respect to x. Use the chain rule on the left and the product rule on the right:(1/y) * dy/dx = (d/dx(tan x)) * ln x + tan x * (d/dx(ln x))(1/y) * dy/dx = sec2x * ln x + tan x * (1/x)Multiply both sides by y:dy/dx = y * (sec2x * ln x + tan x / x)Substitute y = xtan x back:dy/dx = xtan x * (sec2x * ln x + tan x / x)This matches option D.

Hint

When differentiating functions of the form f(x)g(x), always use logarithmic differentiation.

Question Info