# how to find f(x)=2x-tanx pls help

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• February 20th 2011, 12:38 AM
dead24
how to find f(x)=2x-tanx pls help
I really dont know where to post this but i just want to find how to get this:
given: x=1

f(x)=2x-tanx

the answer is supposed to be 0.443.

Now my problem is how did he get 0.433 because i keep doing 2(1)-tan(1) and im getting 1.982544935 HELP IM NOT GOOD AT MATH(Crying)
• February 20th 2011, 12:59 AM
Sudharaka
Quote:

Originally Posted by dead24
I really dont know where to post this but i just want to find how to get this:
given: x=1

f(x)=2x-tanx

the answer is supposed to be 0.443.

Now my problem is how did he get 0.433 because i keep doing 2(1)-tan(1) and im getting 1.982544935 HELP IM NOT GOOD AT MATH(Crying)

You have to consider that x=1 radians to get the desired answer. You had taken x=1 degrees.
• February 20th 2011, 01:07 AM
dead24
im really sorry but how do you do this? im doing 2(pi/180)-tan(pi/180)=0.03496 which is wrong.
• February 20th 2011, 01:15 AM
Sudharaka
Quote:

Originally Posted by dead24
im really sorry but how do you do this? im doing 2(pi/180)-tan(pi/180)=0.03496 which is wrong.

$x~degrees=\left(\frac{pi}{180}\right)x~ rad\longleftrightarrow{x~ rad}=\left(\frac{180}{\pi}\right)x~degrees$

Therefore, $1~rad=\left(\frac{180}{\pi}\right)~degrees$
• February 20th 2011, 03:31 AM
HallsofIvy
Quote:

Originally Posted by dead24
im really sorry but how do you do this? im doing 2(pi/180)-tan(pi/180)=0.03496 which is wrong.

The simplest thing to do is to put your calculator in radian mode and find 2(1)- tan(1).

If your calculator does not have a "radian mode" (which I would find very hard to believe) or you don't know how to set it to radian mode calculate 2(1)- tan(180/pi).

Notice that I have used the "180/pi" to change from radians to degrees only inside the tangent function because it is only inside trig functions that degrees or radians are used.

The calculator that comes with Windows has "Degree", "Radian", and "Grads" buttons on the right just below the number entry window.