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
theorem:\u00a0<\/b>if v(x)\u00a0is a continuous function with an antiderivative v(x),\u00a0<\/i><\/i>then \u00a0where <\/i>, <\/i>\u00a0are in the domain of v(x).\u00a0<\/i><\/i><\/p>\n
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 ‘=
<\/p>\n
we used this to find that the integral ,\u00a0and since we only need one antiderivative to evaluate definite integrals, we can take \u00a0for use in this case.<\/p>\n
therefore we can evaluate (using the fact that\u00a0,\u00a0
,\u00a0
\u00a0and the ftc):<\/p>\n
you can use your calculator to get 723.823 units cubed.<\/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 , 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
from the upper volume, with radius :<\/p>\n
so the answer is a.
\nto compute the value of the integral we see that
\n<\/a><\/p>\n