# Thread: Trigonometry Problems

1. ## Trigonometry Problems

Here are a few Trig problems that I am having trouble with. Any help is greatly appreciated...

-Andrew

1. How many times more intense is a 7.1 richter earthquake than a 6.2 richter quake.
R = log (I/O)

2. Evaluate the value of each indicated trig function (SHOW ALL WORK). I can do this one, but I always forget to show all of my work...

If cos(B) = 4/5, and 3pi/2 < B < 2pi... Find Cot(-B), Cos(2B), and sin(2B)

3. Answer the question by decoding the message, Show all work...
What was trig?
Message encoded using A= [2 5]
1 3
38,105,23,69,21,62,20,60,21,55,2,6,29,82,40,100,36 ,93,20,60,31,84,29,82

2. Originally Posted by Liquidpyro911
Here are a few Trig problems that I am having trouble with. Any help is greatly appreciated...

-Andrew

1. How many times more intense is a 7.1 richter earthquake than a 6.2 richter quake.
R = log (I/O)
We need to solve the above equation for intensity

$10^R=\frac{I}{O} \iff I =O \cdot 10^R$

Now pluging in our values gives

$I_1=O \cdot 10^{7.1}$

$I_2=O \cdot 10^{6.2}$

Now we divide the two

$\frac{I_1}{I_2}=\frac{O \cdot 10^{7.1}}{O \cdot 10^{6.2}} \approx 7.94$

Please show us what you have tried for the other two.

3. I finished #2, but I just have no idea how to do number 3...

Thanks for the help with the first one... btw...

4. Originally Posted by Liquidpyro911
I finished #2, but I just have no idea how to do number 3...

Thanks for the help with the first one... btw...
I'm assuming the matrix for number 3 is

$\left[\begin{array}{cc}
2 & 5\\
1 & 3
\end{array}\right]$
.

It seems to me that the message was encoded using this simple algorithm:

1. Convert all letters to numerical values, with 0 = space, 1 = A, 2 = B, etc
2. Store each pair of values in a 1×2 row matrix
3. Multiply each uncoded row matrix on the right by $A$ to form a coded row matrix
4. List the values in the coded row matrices, in order and without the matrix notation, to form the coded message

All you have to do is repeat this process in reverse (hint: you will need to find $A^{-1}$).