Wyatt Ryder
New member
So for math, we are to come up with the proof for the cosine angle sum identity, i.e. Cos (A+B)= CosA*CosB - SinA*SinB.
To do this, we are only allowed to use the following identities:
1. Sin(A+B)= SinA*CosB + CosA*SinB
2. CosX= Sin(90-X)
3. SinX= Cos (90-X)
4. Cos (-X)= CosX
5. Sin (-X)= -SinX
Could someone please help!? I am so confused on how to do this... the teach gave us a hint and told us to start from here, but I am not sure what to do next:
Cos(A+B)= Sin (90-A-B)
Thank you so much!!!
To do this, we are only allowed to use the following identities:
1. Sin(A+B)= SinA*CosB + CosA*SinB
2. CosX= Sin(90-X)
3. SinX= Cos (90-X)
4. Cos (-X)= CosX
5. Sin (-X)= -SinX
Could someone please help!? I am so confused on how to do this... the teach gave us a hint and told us to start from here, but I am not sure what to do next:
Cos(A+B)= Sin (90-A-B)
Thank you so much!!!