Topic explanation

Standard explanation

cos even: cos(-B)=cos B. sin odd: sin(-B)=-sin B. So the + in the difference law becomes a - between the sin product.

Key points

• even/odd
• cos(A+B)=cos A cos B - sin A sin B
• sin(A+B)=sin A cos B + cos A sin B
• sine plus, cosine minus
• COSINE OF A SUM: cos even: cos(-B)=cos B. sin odd: sin(-B)=-sin B. So the + in the difference law becomes a - between
• COS(A+B): cos even: cos(-B)=cos B.
• WHAT — COSINE OF A SUM: cos even: cos(-B)=cos B. sin odd: sin(-B)=-sin B. So the + in the difference law becomes a - between
• WHY — Why it matters: This rule is a separate learning unit inside compound angles: cos and sin of sums. It can be defined

Labelled diagram