bonjour
rappels du cours
cos (x + 2n π) = cos x ; cos (x + π) = - cos x
cos (π/6) = √3/2 ; cos(π/3) = 1/2
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cos(13π/6) = cos(π/6 + 12π/6) = cos(π/6 + 2π) = cos(π/6) = √3/2
cos(10π/3) = cos(π/3 + 9π/3) = cos(π/3 + 3π)
= cos(π/3 + π + 2 π)
= cos(π/3 + π)
= - cos(π/3)
= - 1/2
(on enlève 2π autant de fois que cela est possible)
