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November 9th, 2016, 05:35 AM  #1 
Member Joined: Aug 2016 From: South Korea Posts: 55 Thanks: 0  Function! Explain please!
Our teacher showed us the answer to f(tanx), if f(b) = b  b^2/1 + b but I don't quite get it.. Someone explain to me how do you get answer for f(tanx), if f(b) = b  b^2/1 + b ?? Last edited by SlayedByMath; November 9th, 2016 at 05:57 AM. 
November 9th, 2016, 05:50 AM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,700 Thanks: 2682 Math Focus: Mainly analysis and algebra 
Your notation doesn't make sense. $f(3)$ must be equal to something.

November 9th, 2016, 05:56 AM  #3 
Member Joined: Aug 2016 From: South Korea Posts: 55 Thanks: 0 
Oh no sorry!! I've typed totally wrong!! >< It's f(b) = b  b^2/ 1 + b then find just only f(tanx) 
November 9th, 2016, 06:02 AM  #4 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,700 Thanks: 2682 Math Focus: Mainly analysis and algebra 
For $f(\tan x)$ you replace $b$ with $\tan x$ wherever it appears.

November 9th, 2016, 06:19 AM  #5 
Member Joined: Aug 2016 From: South Korea Posts: 55 Thanks: 0 
then..? I just saw some tan, sin, cos on the board but I don't actually know how they actually got it? Explain briefly TT.TT 
November 9th, 2016, 07:01 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 21,127 Thanks: 2336 
If f(b) = (b  b^2)/(1 + b) was intended, f(tan(x)) = tan(x)(1  tan(x))/(1 + tan(x)) = tan(x)tan(pi/4  x). 

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