Question

Problem with trigonometric functions.

Answer 1

@thomaster @KingGeorge

Answer 2

sin(a+b) = sinacosb + cosasinb equation 1
sin(a-b)= sinacobl - cosasinb equation 2
cos(a+b)= cosacosb-sinasinb equation 3

sinb =-3/5 put the value in the formula below find cosb
cosb=SQRT(1-sinb^2)

tana = 2/4 = 1/2
put the value in equation below and rearrange to get cos 2a
tana^2= (1-cos2a)/(1+cos2a)
substitute cos2a in this formula and you find cosa
cosa=SQRT((1+cos2a)/2)
substitute cosa into this equation to find sina
sina =SQRT(1-cosa^2)
Now you have all values and substitue in equations 1.2.3