# Math Help - Sum and diffrence Formulas

1. ## Sum and diffrence Formulas

2. k well i got 11, but still stuck on the other 2.

for 10 sin(A+B) i got -84/85 but it says im wrong!!! am i? im sure its -84/85. but i did get the cos which was 77/85..

3. I'd like to help but can't see your questions???

5. woot i got them all... just 1 prob left which i dont know...

Find the exact value of the following.
sin(165°) =

so its somthing to deal with breaking it up into 2

so it would be like 90-30-45 adn then the 90 cancels out and you find the sin of 30 and 45 and u liek mutiply or somthing i forget. can someone help me on this. and no u cant put this in the calculator..

6. If I understand correctly then you would be looking for values on your trig circle (pi/2, pi) and then finding the sin values (sqrt2/2 for example.)

step 1) find what 30 and 40 degrees are equal to on the trig circle

step 2) get both sin values

step 3) multiply them both

I believe this is the correct path to follow

7. Not too sure abut the previous reply????
Have a go at this:
Sin 165 = sin (90+75) = cos 75 (from the unit circle).
Then cos 75 = cos(45+30) and use you cos(a+b) rule.