
Algebra PreAlgebra and Basic Algebra Math Forum 
 LinkBack  Thread Tools  Display Modes 
November 27th, 2014, 01:53 PM  #1 
Newbie Joined: Nov 2014 From: London Posts: 21 Thanks: 0  How did they get this answer?
L=10log(80/1x10^12) L=139.03dB 
November 27th, 2014, 02:32 PM  #2 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,913 Thanks: 1113 Math Focus: Elementary mathematics and beyond 
What is "dB"?

November 27th, 2014, 02:51 PM  #3 
Newbie Joined: Nov 2014 From: London Posts: 21 Thanks: 0  Last edited by greg1313; November 27th, 2014 at 02:54 PM. 
November 27th, 2014, 02:58 PM  #4 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,913 Thanks: 1113 Math Focus: Elementary mathematics and beyond 
Evaluating with a calculator, $\displaystyle 10\log\left(\frac{80}{10^{12}}\right)\approx139.03$
Last edited by greg1313; November 27th, 2014 at 03:17 PM. 
November 27th, 2014, 02:59 PM  #5 
Newbie Joined: Nov 2014 From: London Posts: 21 Thanks: 0  
November 27th, 2014, 03:01 PM  #6 
Math Team Joined: Jul 2011 From: Texas Posts: 2,820 Thanks: 1464  
November 27th, 2014, 03:08 PM  #7 
Banned Camp Joined: Jun 2014 From: Earth Posts: 945 Thanks: 191  SeanDean, you need grouping symbols around the denominator. Here, "log" is taken to be to base 10. "dB" stands for "decibels." L = 10log{80/[1 x 10^(12)]} dB L = 10log{80/[10^(12)]} dB L = 10log(80*10^12) dB L = 10log(8*10*10^12) dB L = 10log(8*10^13) dB L = {10[log(8) + log(10^13)]} dB L = {10log(8) + 10log(10^13)} dB L = [10log(8) + 10(13)] dB L ~ [10(0.90309) + 130] dB L ~ (9.0309 + 130) dB L = 139.03 dB $\displaystyle \ \ \ $when rounded to two decimal places That calculator is off, or possibly you copied that last digit incorrectly. Last edited by Math Message Board tutor; November 27th, 2014 at 03:11 PM. 
November 27th, 2014, 03:17 PM  #8 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,913 Thanks: 1113 Math Focus: Elementary mathematics and beyond  

Tags 
answer 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Need help with this. Can't get the answer  hamburgertime  Algebra  10  February 17th, 2013 08:32 PM 
How do you get this answer 1 + AB/A+B + (A1/A) = A (B + 1)  jon  Algebra  14  October 17th, 2012 05:41 PM 
numeric entry problem with answer..but I think the answer is  rage  Algebra  2  September 14th, 2012 10:27 PM 
i need an answer ...  mimi  Linear Algebra  2  November 30th, 2009 10:43 AM 
Please answer for me  tobymac  Algebra  12  May 23rd, 2009 07:19 PM 