addition formula proof
sin(a+b)= sina x cosb + sinb x cosa
cos(a+b)=cosa x cosb - sina x sinb
cos(a+b)=cosa x cosb - sina x sinb
subtraction formula proof
sin(a-b)=sina x cosb - sinb x cosa
cos(a+b)=cosa x cosb - sina x sinb
cos(a+b)=cosa x cosb - sina x sinb
wait! where's tangent?
By understanding that the value of Tangent is Sine/Cosine we can state that tan(a+b)= sin(a+b)/cos(a+b) and Tan(a-b)=sin(a-b)/cos(a-b)