SOLUTIONS TO DIFFERENTIATION OF TRIGONOMETRIC FUNCTIONS



SOLUTION 1 : Differentiate tex2html_wrap_inline228 .

(Recall that tex2html_wrap_inline230. The product rule is NOT necessary here.)

Then

tex2html_wrap_inline232

tex2html_wrap_inline234

tex2html_wrap_inline236 .

Click HERE to return to the list of problems.




SOLUTION 2 : Differentiate tex2html_wrap_inline238 . Apply the product rule.

Then

tex2html_wrap_inline240

tex2html_wrap_inline242

tex2html_wrap_inline244 .

Click HERE to return to the list of problems.




SOLUTION 3 : Differentiate tex2html_wrap_inline246 . Apply the quotient rule.

Then

tex2html_wrap_inline248

tex2html_wrap_inline250

tex2html_wrap_inline252

tex2html_wrap_inline254

(Recall the well-known trigonometry identity tex2html_wrap_inline256.)

tex2html_wrap_inline258

tex2html_wrap_inline260

tex2html_wrap_inline262 .

Click HERE to return to the list of problems.




SOLUTION 4 : Differentiate tex2html_wrap_inline264 . Apply the product rule.

Then

tex2html_wrap_inline266

tex2html_wrap_inline268

tex2html_wrap_inline270

tex2html_wrap_inline272 .

Click HERE to return to the list of problems.




SOLUTION 5 : Differentiate tex2html_wrap_inline274 . To avoid using the chain rule, first rewrite the problem as

tex2html_wrap_inline274

tex2html_wrap_inline278

tex2html_wrap_inline280

tex2html_wrap_inline282

tex2html_wrap_inline284 .

Now apply the product rule. Then

tex2html_wrap_inline286

tex2html_wrap_inline288

tex2html_wrap_inline290 .

Click HERE to return to the list of problems.




SOLUTION 6 : Differentiate tex2html_wrap_inline292 . To avoid using the chain rule, recall the trigonometry identity tex2html_wrap_inline294, and first rewrite the problem as

tex2html_wrap_inline292

tex2html_wrap_inline298 .

Now apply the product rule twice. Then

tex2html_wrap_inline300

tex2html_wrap_inline302

tex2html_wrap_inline304

(This is an acceptable answer. However, an alternative answer can be gotten by using the trigonometry identity tex2html_wrap_inline306.)

tex2html_wrap_inline308

tex2html_wrap_inline310

tex2html_wrap_inline312 .

Click HERE to return to the list of problems.




SOLUTION 7 : Differentiate tex2html_wrap_inline314 . Rewrite g as a triple product and apply the triple product rule. Then

tex2html_wrap_inline314

tex2html_wrap_inline320

so that the derivative is

tex2html_wrap_inline322

tex2html_wrap_inline324

tex2html_wrap_inline326 .

Click HERE to return to the list of problems.




SOLUTION 8 : Evaluate tex2html_wrap_inline328 . It may not be obvious, but this problem can be viewed as a differentiation problem. Recall that

tex2html_wrap_inline330 .

If tex2html_wrap_inline332 , then tex2html_wrap_inline334, and letting tex2html_wrap_inline336 it follows that

tex2html_wrap_inline338

tex2html_wrap_inline340

tex2html_wrap_inline342

tex2html_wrap_inline344 .

Click HERE to return to the list of problems.




SOLUTION 9 : Differentiate tex2html_wrap_inline346 . Apply the chain rule to both functions. (If necessary, review the section on the chain rule .) Then

tex2html_wrap_inline348

tex2html_wrap_inline350

tex2html_wrap_inline352

(Recall that tex2html_wrap_inline294.)

tex2html_wrap_inline356

tex2html_wrap_inline358 .

Click HERE to return to the list of problems.




SOLUTION 10 : Differentiate tex2html_wrap_inline360 . This is NOT a product of functions. It's a composition of functions. Apply the chain rule. Then

tex2html_wrap_inline362

tex2html_wrap_inline364 .

Click HERE to return to the list of problems.




SOLUTION 11 : Differentiate tex2html_wrap_inline366 . Apply the quotient rule first, followed by the chain rule. Then

tex2html_wrap_inline368

tex2html_wrap_inline370

tex2html_wrap_inline372

tex2html_wrap_inline374 .

Click HERE to return to the list of problems.




SOLUTION 12 : Differentiate tex2html_wrap_inline376 . Apply the product rule first, followed by the chain rule. Then

tex2html_wrap_inline378

tex2html_wrap_inline380

tex2html_wrap_inline382

tex2html_wrap_inline384

tex2html_wrap_inline386 .

Click HERE to return to the list of problems.




SOLUTION 13 : Differentiate tex2html_wrap_inline388 . Apply the chain rule four times ! Then

tex2html_wrap_inline390

tex2html_wrap_inline392

tex2html_wrap_inline394

tex2html_wrap_inline396

tex2html_wrap_inline398 .

Click HERE to return to the list of problems.




SOLUTION 14 : Differentiate tex2html_wrap_inline400 . Apply the quotient rule first. Then

tex2html_wrap_inline402

(Apply the product rule in the first part of the numerator.)

tex2html_wrap_inline404

tex2html_wrap_inline406

tex2html_wrap_inline408

tex2html_wrap_inline410

tex2html_wrap_inline412 .

Click HERE to return to the list of problems.




SOLUTION 15 : Find an equation of the line tangent to the graph of tex2html_wrap_inline414 at x=-1 . If x= -1 then tex2html_wrap_inline420 so that the tangent line passes through the point (-1, 0 ) . The slope of the tangent line follows from the derivative

tex2html_wrap_inline424

tex2html_wrap_inline426 .

The slope of the line tangent to the graph at x = -1 is

tex2html_wrap_inline430

tex2html_wrap_inline432

tex2html_wrap_inline434

= -2 .

Thus, an equation of the tangent line is

y - 0 = -2 (x - (-1) ) or y = -2x - 2 .

Click HERE to return to the list of problems.




SOLUTION 16 : Find an equation of the line perpendicular to the graph of tex2html_wrap_inline442 at tex2html_wrap_inline444 . If tex2html_wrap_inline444 then tex2html_wrap_inline448 tex2html_wrap_inline450 so that the tangent line passes through the point tex2html_wrap_inline452 . The slope of the tangent line follows from the derivative of y . Then

tex2html_wrap_inline456

tex2html_wrap_inline458

tex2html_wrap_inline460

tex2html_wrap_inline462 .

The slope of the line tangent to the graph at tex2html_wrap_inline444 is

tex2html_wrap_inline466

tex2html_wrap_inline468

tex2html_wrap_inline470 .

Thus, the slope of the line perpendicular to the graph at tex2html_wrap_inline444 is

m = - 2 ,

so that an equation of the line perpendicular to the graph at tex2html_wrap_inline444 is

tex2html_wrap_inline478 or tex2html_wrap_inline480 .

Click HERE to return to the list of problems.




SOLUTION 17 : Assume that tex2html_wrap_inline482 . Solve f'(x) = 0 for x in the interval tex2html_wrap_inline486 . Use the chain rule to find the derivative of f . Then

tex2html_wrap_inline490

tex2html_wrap_inline492

tex2html_wrap_inline494

(It is a fact that if A B = 0 , then A=0 or B = 0 . )

so that

tex2html_wrap_inline502 or tex2html_wrap_inline504 .

If tex2html_wrap_inline502 , then the only solutions x in tex2html_wrap_inline486 are

tex2html_wrap_inline512 or tex2html_wrap_inline514 .

If tex2html_wrap_inline504 , then the only solutions x in tex2html_wrap_inline486 are

tex2html_wrap_inline522 or tex2html_wrap_inline524 .

Thus, the only solutions to f'(x) = 0 in the interval tex2html_wrap_inline486 are

tex2html_wrap_inline530 or tex2html_wrap_inline514 .

Click HERE to return to the list of problems.




SOLUTION 18 : Use any method to verify that tex2html_wrap_inline534 .

Then

tex2html_wrap_inline536

(Apply the quotient rule.)

tex2html_wrap_inline538

tex2html_wrap_inline540

tex2html_wrap_inline542

(Recall the well-known trigonometry identity tex2html_wrap_inline256.)

tex2html_wrap_inline546

(Recall that tex2html_wrap_inline548.)

tex2html_wrap_inline550

tex2html_wrap_inline552

tex2html_wrap_inline554 .

Click HERE to return to the list of problems.







Duane Kouba
Sun Aug 3 18:53:29 PDT 1997