Trigonométrie (5ème)

= cos(a) . cos(b) - sin(a) . sin(b)

= cos(a) . cos(b) + sin(a) . sin(b)

= sin(a) . cos(b) + cos(a) . sin(b)

= sin(a) . cos(b) - cos(a) . sin(b)

= 2sin(a) . cos(a)

= 2 sin(a) . cos(a)

= cos2a - sin2a