Additional formulae
cos(A-B)=cosAcosB+sinAsinB
cos(A+B)=cosAcosB-sinAsinB
sin(A+B)=sinAcosB+cosAsinB
sin(A-B)= sinAcosB-cosAsinB
tan(A+B)=

tan(A-B)=

Ex 5B
2)
a) cos 105
o cos (60+45) = cos60.cos45- sin60.sin45
=1/2. 1/

-

/2. 1/

=1/2

-

/2

= 1-3/ 2

=

-

/ 4
4) sin(3/2pi + x)
= sin3/2picosx+ cos3/2pisinx
=-1cosx+0sinx
=-1cosx