Math Is Fun Forum

***SOLVED***

I have two more questions about this section that are a little shady -

>>>>"Suppose that cos A = 0.6 and sin A = 0.8.  Suppose that cos B = 0.96 and sin B = 0.28.  Use the composite argument property to find cos (A + B)."

I responded with
cos (A − B) = cos A cos B + sin A sin B
cos(A-B)=0.6*0.96+0.8*0.28
cps(A-B)=0.576+0.224
cos(A+B)=0.129024

arccos0.129024=A+B
A+B=1.441411637

...I'm pretty sure this is correct, but a double check would be greatly appreciated ... so far so good, until-

>>>>"Show that cos -10.6 and sin-10.8 give the same degree measure for angle A."

How am I suppose to use the "composite argument property" to answer this question? (If I'm suppose to use it, it does not say so but it is in the same section...) All I did was punch both of these in my calculator to prove that they have the same degree measure. Surely I cannot put this as an answer, my instructor will think I'm being a smart ---. Here's another just like it-

>>>>"Show that both cos-1 0.96 and sin -1 0.28 give the same degree measure for angle B."

Any geniuses out there willing to help would be greatly appreciated :D