Salut,
sin x = 4/5
cos y = -3/5
x ; y € C II
sin²x+cos²x = 1
16/25+cos²x = 1
cos²x = 9/25
cos x = -3/5.
sin²y+cos²y = 1
sin²y+9/25 = 1
sin²y = 16/25
sin y = 4/5.
sin(x-y) = sin x • cos y - sin y • cos x
= 4/5•(-3/5)-4/5•(-3/5) = -12/5+12/5 = 0.
sin 2x = 2sin x • cosx = 2•4/5•(-3/5) = -8/5•3/5 = -24/25.
Succes! :3
