a) 3sinx/2-cosx-4=0
b) cosx/2-cosx-2=0
c) sin^2 x/2 -cosx-2=0
d) cos2x+4cosx-5=0
a) 3sinx/2-cosx-4=0 b) cosx/2-cosx-2=0 c) sin^2 x/2 -cosx-2=0 d) cos2x+4cosx-5=0
By Jasmine
By Jasmine
a) 3sinx/2-cosx-4=0
b) cosx/2-cosx-2=0
c) sin^2 x/2 -cosx-2=0
d) cos2x+4cosx-5=0
Đáp án:
cos 2x – 4 cos x – 5 = 0
(2 cos^2 x – 1) – 4 cos x – 5 = 0
2 cos^2 x – 4 cos x – 6 = 0
cos^2 x – 2 cos x – 3 = 0
(cos x – 3)(cos x + 1) = 0
cos x – 3 = 0 or cos x + 1 = 0
cos x = 3 (reject)…..cos x = -1
…………………………..x = π
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