My Math Forum Find area

 Calculus Calculus Math Forum

 January 18th, 2010, 04:08 PM #1 Senior Member   Joined: Nov 2009 Posts: 169 Thanks: 0 Find area Find the area between the graph of f and the x-axis. $f(x)= x^3 + 1, x\in [-2, -1].$ $\int _{-2}\,^{-1}\!x^3+1dt$
 January 18th, 2010, 04:14 PM #2 Member   Joined: Dec 2009 Posts: 31 Thanks: 0 Re: Find area Just take the definite integral of f(x) from -2 to -1 (your final answer will be 11/3).
January 18th, 2010, 04:37 PM   #3
Senior Member

Joined: Nov 2009

Posts: 169
Thanks: 0

Re: Find area

Quote:
 Originally Posted by Erebos Just take the definite integral of f(x) from -2 to -1 (your final answer will be 11/3).

I got 4/7 as my final answer, do I need a minus sign in front of the integral, the anti deritavitive I got is $1/4x^4 + x$

 January 18th, 2010, 05:15 PM #4 Senior Member   Joined: Aug 2008 From: Blacksburg VA USA Posts: 347 Thanks: 6 Math Focus: primes of course Re: Find area well, Wolframalpha gives -11/4 ...
January 18th, 2010, 05:19 PM   #5
Senior Member

Joined: Nov 2009

Posts: 169
Thanks: 0

Re: Find area

Quote:
 Originally Posted by billymac00 well, Wolframalpha gives -11/4 ...

Can you show me how you got that, what is the anti derivative you got?

 January 18th, 2010, 05:21 PM #6 Senior Member   Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3 Re: Find area $\int_{-2}^{-1}x^3+1 dx= \left[ \frac14 x^4+x \right]_{-2}^{-1} = (\frac14 (-1)^4 - 1) - (\frac14 (-2)^4 - 2) = (-\frac34)-(2) = -\frac{11}{4}$
 January 18th, 2010, 05:25 PM #7 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,945 Thanks: 1136 Math Focus: Elementary mathematics and beyond Didn't see the above.
January 19th, 2010, 02:45 AM   #8
Global Moderator

Joined: Dec 2006

Posts: 20,747
Thanks: 2133

Quote:
 Originally Posted by 450081592 do I need a minus sign in front of the integral
The area lies entirely "below" the x-axis, so you should put a minus sign in front of the integral.

 Tags area, find

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post johnny993 Algebra 1 November 12th, 2013 09:17 PM gelatine1 Algebra 13 January 4th, 2013 10:42 AM Albert.Teng Algebra 2 July 21st, 2012 12:17 AM Arley Calculus 3 April 28th, 2012 09:22 AM seit Calculus 4 November 14th, 2010 05:48 AM

 Contact - Home - Forums - Cryptocurrency Forum - Top