Thread: trig 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 ??

Originally Posted by gregorio

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 ??

there are several ways to approach this

you can note that:



and



OR

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

OR

you can use the double angle formula:

........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