Bonjour
Pour tout réel x et pour tout entier k,
[tex] \cos(x + 2k\pi) = \cos(x) [/tex]
[tex] \sin(x + 2k\pi) = \sin(x) [/tex]
cos(100π) = cos(0 + 2 × 50π) = cos(0) = 1
sin(300π) = sin(0 + 2 × 150π) = sin(0) = 0
-cos(7π/3) = - cos ( 6π/3 + π/3 ) = - cos ( π/3 + 2π )
= - cos(π/3) = -1/2
cos(203π) = cos(π + 2 × 101π) = cos π = -1
sin 27π/2 = sin ( 28π/2 - π/2 ) = sin(-π/2 + 2 × 14π)
= sin -π/2 = -1
- sin π/6 = -1/2
donc ça fait ( 1 + 0 - 1/2 ) ( -1 -1 - 1/2 )
= - 1/2 ( 5/2 ) = -5/4 = -1,25
