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MTH 102 MTH 102 Past Questions Objective Question

Question

Find dy/dx if y = xtan x.
Options
A <i>dy/dx = -x<sup>tan x</sup> (tan x / x - sec<sup>2</sup> x ln x)</i>
B <i>dy/dx = -x<sup>tan x</sup> (tan x / x + sec<sup>2</sup> x ln x)</i>
C <i>dy/dx = x<sup>tan x</sup> (tan x / x - sec<sup>2</sup> x ln x)</i>
D <i>dy/dx = 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 problem requires logarithmic differentiation because the variable x appears in both the base and the exponent.1. Take the natural logarithm of both sides: ln y = ln(xtan x) = tan x * ln x.2. Differentiate both sides with respect to x. Use the product rule on the right side:(1/y) dy/dx = (d/dx tan x) * ln x + tan x * (d/dx ln x)(1/y) dy/dx = (sec2 x) * ln x + tan x * (1/x)3. Multiply by y to solve for dy/dx:dy/dx = y * ( (sec2 x) ln x + tan x / x )4. Substitute y = xtan x back into the equation:dy/dx = xtan x * ( (sec2 x) ln x + tan x / x )This matches option D.

Hint

When the variable appears in both the base and the exponent, logarithmic differentiation is the key. Take the natural logarithm of both sides, then differentiate implicitly.

Question Info