<p>this is the sum formula right?
but whats getting me confused is this has an extra variable
how am i suppose to prove it ?
sin(x+y+z)=sinXcosYcosZ+cosXsinYcosZ+cosXcosYsinZ-sinXsinYsinZ</p>
<p>umm, I never knew there’s a formula like that. the one that i know is: sin(x+y)=sinxcosy+cosxsiny</p>
<p>I didn’t know either of those formulas. 
I feel stupid.</p>
<p>Those formulas **** me off more than everything that it can’t just be easier.</p>
<p>sin(x+y+z) = sin(x+(y+z))
= sin(x)cos(y+z) + cos(x)sin(y+z)
= sin(x)[cos(y)cos(z) - sin(y)sin(z)] + cos(x)[sin(y)cos(z) + cos(y)sin(z)]
= sin(x)cos(y)cos(z) - sin(x)sin(y)sin(z) + cos(x)sin(y)cos(z) + cos(x)cos(y)sin(z)</p>
<p>or</p>
<p>sin(x+y+z) = sin((x+y)+z)
= sin(x+y)cos(z) + cos(x+y)sin(z)
= [sin(x)cos(y) + cos(x)sin(y)]cos(z) + [cos(x)cos(y) - sin(x)sin(y)]sin(z)
= sin(x)cos(y)cos(z) + cos(x)sin(y)cos(z) + cos(x)cos(y)sin(z) - sin(x)sin(y)sin(z)</p>
<p>:)</p>
<p>lol, the orignal poster added cosXcosYsinZ-sinXsinYsinZ.
follow kemet’s proof. he got it.</p>
<p>thanks alot</p>
<p>i hated all those random rules…double angle, half angle, angle sum…gah! it got annoying! luckily i had a teacher who was like " i dont have em memorized, you dont need to, you can just have a notecard"
for those things</p>
<p>Ooh logistics that’s no good if you’re going to take the AP Calculus test…ETS has been known to bring stuff like that up.</p>
<p>ey ey ey…not taking ap calc test! only 1-2/30 kids in my class are…plus they havent even come up in ap calc yet, so im fine with not knowing them.</p>