{"id":10269,"date":"2017-06-19t15:10:20","date_gmt":"2017-06-19t22:10:20","guid":{"rendered":"\/\/www.catharsisit.com\/hs\/?p=10269"},"modified":"2017-06-18t16:13:38","modified_gmt":"2017-06-18t23:13:38","slug":"ap-calculus-bc-review-integration-substitution","status":"publish","type":"post","link":"\/\/www.catharsisit.com\/hs\/ap\/ap-calculus-bc-review-integration-substitution\/","title":{"rendered":"ap calculus bc review: integration by substitution"},"content":{"rendered":"
substitution<\/strong> is just one of the many techniques available for finding indefinite integrals<\/em> (that is, antiderivatives<\/em>). let’s review the method of integration by substitution and get some practice for the ap calculus bc exam.<\/p>\n integration by substitution, also known as u<\/em>-substitution<\/strong>, after the most common variable for substituting, allows you to reduce a complicated integral to one that is easier to work with.<\/p>\n the formula works as follows. suppose that f<\/em> is an antiderivative for f<\/em>. then we have:<\/p>\n in fact, you can think of the substitution rule as reversing the chain rule<\/em>.<\/p>\n basically, this rule states that if you have a complicated integral like the one on the left, then it instantly reduces to a simpler one that can be worked out with no trouble.<\/p>\n however, the hard part is arranging a given integral in the right way. that’s where the step-by-step method outlined below comes in.<\/p>\n furthermore, substituting isn’t a magic bullet that can tackle every integral. just think of it as one powerful tool in your toolbox. for more tools and information about integration, check out the following resource. ap calculus review: indefinite integrals<\/a>.<\/p>\n next let’s review the main steps in u<\/em>-substitution.<\/p>\n if you want to use substitution, then the first thing to do is to identify what you want to substitute.<\/p>\n in other words, you have to make a choice for what u<\/em> = g<\/em>(x<\/em>) will be in your integral.<\/p>\n but what should you choose? that comes with experience.<\/p>\n there are a few good rules of thumb to follow when choosing u<\/em>, but these are by no means fool-proof. so if the first choice doesn’t work, try something else.<\/p>\n once you’ve decided on your substitution, the next step is to find its differential<\/strong>. remember, the differential of a function of x<\/em> is just its derivative times dx<\/em>.<\/p>\n so the differential of u<\/em> = g<\/em>(x<\/em>) is du<\/em> = g<\/em>\u00a0‘(x<\/em>)\u00a0dx<\/em>,<\/p>\n the reason you should do this step is that the differential provides a link between the “dx<\/em>” from the original integral and the new integral, which will have “du<\/em>” instead.<\/p>\n now you get to change the form of the integral.<\/p>\n replace g<\/em>(x<\/em>) by u<\/em>, hopefully making the integrand a little simpler.<\/p>\n but don’t be worried if there are still expressions in the integral involving x<\/em>. in fact, those leftover expressions can be traded out using du<\/em> = g<\/em>\u00a0‘(x<\/em>)\u00a0dx<\/em>.<\/p>\n the only catch is that you have to have a perfect<\/em> match in order to make the trade. we’ll see more about this point in the examples below.<\/p>\n next, check to see what variables are represented in the integral. if there are any leftover x<\/em>‘s anywhere, or if the old differential dx<\/em> is still in the integral, then the substitution is not complete.<\/p>\n however if there are only expressions of u<\/em>, and if the differential is du<\/em>, then you can move on to the integration step.<\/p>\nthe substitution rule<\/h2>\n
<\/p>\n
the method of integration by substitution<\/h2>\n
step 1. choose your substitution<\/h3>\n
\n
step 2. find the differential<\/h3>\n
step 3. rewrite the integral<\/h3>\n
step 4. simplify and integrate<\/h3>\n