Find the differential $d y \text { of the function } y = x \cos ( 7 x ) \text {. }$
A) $7 x \sin ( 7 x ) d x$
B) $\cos ( 7 x ) d x$
C) $\cos ( 7 x ) + 7 x \sin ( 7 x ) d x$
D) $\cos ( 7 x ) - 7 x \sin ( 7 x ) d x$
E) $- 7 x \sin ( 7 x ) d x$

Question

Find the differential $d y \text { of the function } y = x \cos ( 7 x ) \text {. }$ 
A) $7 x \sin ( 7 x ) d x$
B) $\cos ( 7 x ) d x$
C) $\cos ( 7 x ) + 7 x \sin ( 7 x ) d x$
D) $\cos ( 7 x ) - 7 x \sin ( 7 x ) d x$
E) $- 7 x \sin ( 7 x ) d x$

Quizplus · Accepted Answer

The derivative of $y = x \cos ( 7 x ) $ is $$d y = \frac{d}{d x} [x \cos ( 7 x )] = x \frac{d}{d x} [\cos ( 7 x )] + \cos ( 7 x ) \frac{d}{d x} [x] = -7 x \sin ( 7 x ) + \cos ( 7 x ).$$

Find the Differential dy of the function y=xcos⁡(7x). d y \text { of the function } y = x \cos ( 7 x ) \text {. }dy of the function y=xcos(7x).

Find the Differential $d y \text { of the function } y = x \cos ( 7 x ) \text {. }$