# Trigonometry converting degrees

• Mar 29th 2010, 12:43 PM
Trigonometry converting degrees
Hi guys, Thanks for all help in advance.

A question requires me to find t in seconds.

h = 13 m

13 = -10 cos (πt/15) + 11.

13-11/-10 = cos (πt/15)

cos^-1(1/5) = 78.5

78.5 = πt/15

...

is what im doing right so far? im required to convert 78.5 degrees to seconds, im unsure how to do this. =(
• Mar 29th 2010, 02:03 PM
mathemagister
Quote:

Hi guys, Thanks for all help in advance.

A question requires me to find t in seconds.

h = 13 m

13 = -10 cos (πt/15) + 11.

13-11/-10 = cos (πt/15)

cos^-1(1/5) = 78.5

78.5 = πt/15

...

is what im doing right so far? im required to convert 78.5 degrees to seconds, im unsure how to do this. =(

If the function you typed is correct, then I think you did a silly arithmetical mistake. $\frac{13-11}{-10} = -\frac{1}{5}$ not 1/5.

So you have:

$cos^{-1}\left(-\frac{1}{5}\right) = \frac{\pi t}{15}$

$101.5 = \frac{\pi t}{15}$

As far as converting 101.5 degrees to seconds? You would just multiply 101.5 by 60*60.

However, I'm not sure if that's what the question is asking. I am assuming that the function is defined as h(t), where h is the height in meters and t is the time in seconds. So, you don't need to convert anything. (I'm just assuming because no normal Math question would ask that.) The answer would just be whatever you solve for t (unless t is not defined as seconds).

Hope that clarified things :)

Mathemagister
• Mar 29th 2010, 02:30 PM
Hi there! (Happy)

so the equation was:

h = -10 cos (πt/15) + 11

h = 13

find t

...

13-11/-10 = -1/5

cos^-1(-1/5) = 101.5

101.5 = πt/15

1522.5/180 = 8.45

t = 8.5 seconds

for the function h, t was defined in seconds. There was no need for conversion.

Appreciate the help.
• Mar 29th 2010, 02:38 PM
mathemagister
Quote:

Hi there! (Happy)

so the equation was:

h = -10 cos (πt/15) + 11

h = 13

find t

...

13-11/-10 = -1/5

cos^-1(-1/5) = 101.5

101.5 = πt/15

1522.5/180 = 8.45

t = 8.5 seconds

for the function h, t was defined in seconds. There was no need for conversion.

Appreciate the help.

No problem :)

Just remember to always compare the units the variables are defined in with the units the answer has to be in. Usually, they will be the same and it'll save you work.