Right i think i've done most of question 20a but the books giving me a slightly different answer to what i've got which i'm sure is right.
20a) 1.5 sin2x + 2cos2x
R sin(2x+a) = R sin2x cosa + R sina cos2x
R cos a =1.5
R sin a =2
Rsina/Rcosa=2/1.5
tan a=2/1.5
a=53.13
R=1.5/cosa=2.5
Answer= 2.5sin(2x + 53.13)
however the book seems to think its 2.5sin(2x+0.927)
Anyone got any suggestions?