rewrite 2sin3x-4cos3x-5 into one function for graphing

M

mdem1234

New member
Joined
Apr 6, 2009
Messages
15
Hi guys,

I have this function 2sin3x-4cos3x-5

I need to combine it into one function so I can graph it.

I have R=root (2^2+4^2) = root 20

cos theta= 2/root20, sin theta =4/root20

so theta=1.017

so my combined function is..

root20Sin(3x+1.107)-5

is this correct, I am a bit confused about theta and if it is in degrees or radians, and if it is in degrees, do i need to convert it into radians before i can graph it properly?.... if anyone could help me out that would be much appreciated, thanks :)
 
Re: sin function

Hello, mdem1234!


I have this function: \(\displaystyle 2\sin3x-4\cos3x-5\)

I need to combine it into one function so I can graph it.

I have: \(\displaystyle R\:=\:\sqrt{2^2+4^2} \:=\:\sqrt{20}\)

. . \(\displaystyle \cos\theta\:=\:\frac{2}{\sqrt{20}},\quad\sin\theta \:=\:\frac{4}{\sqrt{20}}\)

so: \(\displaystyle \theta \:\approx\: 1.017\)

So my combined function is: .\(\displaystyle \sqrt{20}\sin(3x+1.107)-5\)

is this correct? . . . . Yes!

I am a bit confused about theta and if it is in degrees or radians.
Click to expand...

You already have \(\displaystyle \theta\) in radians . . . good!

Nearly all advanced math is performed in radians.

. . "When in doubt, use radians."

 
Re: sin function

\(\displaystyle f(x) = \sqrt(20)sin(3x+1.10715)-5, \ Wrong.\)

\(\displaystyle f(x) = \sqrt(20)sin(3x-1.10715)-5, \ Right.\)
 
Re: sin function

BigGlenntheHeavy said:
\(\displaystyle f(x) = \sqrt(20)sin(3x+1.10715)-5, \ Wrong.\)

\(\displaystyle f(x) = \sqrt(20)sin(3x-1.10715)-5, \ Right.\)
Click to expand...


Why is it minus and not plus 1.10715??
 
because your original equation was

2sin3x - 4cos3x - 5
 
You must log in or register to reply here.
Top