{"id":8182,"date":"2016-12-08t11:45:36","date_gmt":"2016-12-08t19:45:36","guid":{"rendered":"\/\/www.catharsisit.com\/hs\/?p=8182"},"modified":"2016-12-02t15:40:21","modified_gmt":"2016-12-02t23:40:21","slug":"computing-definite-integral-polynomial","status":"publish","type":"post","link":"\/\/www.catharsisit.com\/hs\/ap\/computing-definite-integral-polynomial\/","title":{"rendered":"computing the definite integral of a polynomial"},"content":{"rendered":"
we want to focus on the definite integral of a polynomial function. these arise very commonly in calculus, so here are detailed solutions to two problems, one multiple-choice and one free-response, involving a definite integral of polynomial.<\/p>\n
<\/p>\n
you will not commonly be asked to evaluate common definite integrals on the free-response, but rather you will be asked to find an area or compute a volume, which will require computing a common definite integral. suppose we want to compute the volume of the solid obtained by revolving the function about the x-axis:<\/p>\n
the cross sections when cutting perpendicular to the x-axis are circles with radius given by the function\u00a0 therefore to compute the integral we compute the sum of the integrals of the individual terms, since polynomials are sums of continuous functions:<\/p>\n theorem:\u00a0<\/b>if v(x)\u00a0is a continuous function with an antiderivative v(x),\u00a0<\/i><\/i>then the ftc says that we can pick any old antiderivative v(x)<\/em> for v(x)<\/em>, so we need to compute a string of antiderivatives for the integrands of the terms in the sum. in the previous post we discussed but did not state:<\/p>\n the power rule:<\/b> the derivative we used this to find that the integral therefore we can evaluate (using the fact that\u00a0 you can use your calculator to get 723.823 units cubed.<\/p>\n <\/p>\n here is a sample of a typical multiple-choice question asking for you to formulate a definite integral based on the same concept discussed above.<\/p>\n question: <\/b>a solid is generated by revolving the region enclosed by the function the idea for this problem is to recognize that this solid is a difference of integrals. suppose that we had the volume of the function\u00a0 given this volume, we would only need to subtract the volume of the following figure, derived by rotating y=1\u00a0bounded by x=2, x=3,\u00a0about the x-axis:<\/p>\n from the upper volume, with radius therefore we need to subtract the two integrals, however using the integral laws we can express this in the form <\/a><\/p>\n
.\u00a0the definite integral that needs to be evaluated is\u00a0
, \u00a0since this is the area of a circle multiplied by the length of the interval from -6 to 6. we compute:<\/p>\n
<\/a><\/p>\n
<\/a><\/p>\n
recall the fundamental theorem of calculus (ftc):<\/h3>\n
\u00a0where <\/i>, <\/i>\u00a0are in the domain of v(x).\u00a0<\/i><\/i><\/p>\n
‘=
<\/p>\n
,\u00a0and since we only need one antiderivative to evaluate definite integrals, we can take \u00a0for use in this case.<\/p>\n
,\u00a0
,\u00a0
\u00a0and the ftc):<\/p>\n
<\/a><\/p>\n
multiple-choice definite integrals:<\/h2>\n
, and the lines x=2, x=3, y=1\u00a0about the x-axis. which of the following definite integrals gives the volume of the solid? (hint: draw a picture)<\/p>\n
<\/a><\/p>\n
\u00a0when bounded by the lines\u00a0\u00a0x = 2, x = 3,\u00a0and rotated about the x-axis\u2014then we would have the volume of the following solid:<\/p>\n
<\/a><\/p>\n
<\/a><\/p>\n
:<\/p>\n
<\/a><\/p>\n
,\u00a0which we follow up by substitution of our names for
,
:<\/p>\n