if i have cos theta = 0.4

what are the values of

cos (180-theta)

cos (360-theta)

i solve like this

cos.4 inverse = 66.42

therefore cos ( 180-66.42)

i have cos *113.57 is this answer or must i make multiplication which gets me -.4 ??

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- Aug 26th 2007, 07:30 AMgregoriotrig question
if i have cos theta = 0.4

what are the values of

cos (180-theta)

cos (360-theta)

i solve like this

cos.4 inverse = 66.42

therefore cos ( 180-66.42)

i have cos *113.57 is this answer or must i make multiplication which gets me -.4 ?? - Aug 26th 2007, 07:38 AMJhevon
there are several ways to approach this

you can note that:

$\displaystyle \cos (180 - \theta ) = - \cos \theta$

and

$\displaystyle \cos (360 - \theta ) = \cos \theta$

OR

you can do it the way you did, and you would get the same answer

OR

you can use the double angle formula:

$\displaystyle \cos (A - B) = \cos A \cos B + \sin A \sin B$ ........which, by the way, is how we know the first two formulas i gave you

and, by the way, it is NOT cos * 113.57, it is cos(113.57). the cosine function is an argument, you cannot treat it like a term unto itself and multiply it with something