tailieunhanh - Calculus: An Integrated Approach to Functions and their Rates of Change, Preliminary Edition Part 83

Calculus: An Integrated Approach to Functions and their Rates of Change, Preliminary Edition Part 83. A major complaint of professors teaching calculus is that students don't have the appropriate background to work through the calculus course successfully. This text is targeted directly at this underprepared audience. This is a single-variable (2-semester) calculus text that incorporates a conceptual re-introduction to key precalculus ideas throughout the exposition as appropriate. This is the ideal resource for those schools dealing with poorly prepared students or for schools introducing a slower paced, integrated precalculus/calculus course | Substitution to Alter the Form of an Integral 801 3x Let u 2 3 du dx 2 2 so dx du 3 1 dx 1 1 2 - du 1 u2 3 3 4 1 ----- du 1 u2 1 arctan u C - arctan - 22 b f ta x dx Use substitution to get rid of the x. Let u s x. du ----- dx 2 x r 1 f tan V dx I tan u 2du Vx J 2 y tan u du sin u -----du cos u Let W cos u. dW sin u du 1 so 2du dx yx dW This looks essentially like w. dW sin u du sin u -----du 2 cos u 2ln W C Replace W by cos u. 2 ln cos u C -2 ln cos x C Replace u by x. c f 2x22xx i dx j e2x 2ex 1 We want to use substitution to get rid of ex and e2x. If we let u ex then e2x ex 2 u2. If instead we were to let u e2x then ex e2x 1 2 u. The flrst option looks much more appealing. Let s try it. Let u ex . du ex dx e2x e2x 2ex 1 dx 802 CHAPTER 25 Finding Antiderivatives An Introduction to Indefinite Integration Either we can express this as ex x u e dx r-----------du e2x 2ex 1 u2 2u 1 or ex 2 u2 1 11 I ---r--------dx I ----------- du because dx du du ex 2 2ex 1 u2 2u 1 u ex u The two are equivalent. uu du du u 2u 1 u 1 This is a simpler integral than the one we began with but it is awkward. If we could get the sum in the numerator as opposed to the denominator we d be happier. We ll accomplish this with another substitution. Let W u 1 so u W 1. dW du u W - 1 ------t du dW u 1 2 W2 W1 5- dW W2 W2 dW - W 2 dW W ln WI W 1 C Replace W by u 1. 1 ln u 11 - ---- C Replace u by ex. u 1 1 ln e 1 - - - - C e -1 EXERCISE Check the answers to Example by differentiating. PROBLEMS FOR SECTION For Problems 1 through 11 find the given indefinite integral. 1- jqpi Jx 2. f -Vy Jx 3. f xV3x 5 Jx 4- f 32px Jx 5. f 3i Vi2 5 Ji 6. f i V2i 5 Ji Substitution to Alter the Form of an Integral 803 -5 dx 8 cot 3x dx 9. 1 1 dt 10. sin41 cos t dt 11. 2t V2t 6 dt 12. Suppose you ve forgotten the antiderivative of 1 . In this problem you will use a sophisticated substitution that will help you proceed. The goal is to flnd 1 dx. Jo V1 -2 We can t let u x2 or 1 - x2 because u

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