решите уравнение а) 3 sin^{2}x + 7cosx -3=0б) sin^{2}x - cos x sinx =0
1) 2-2cos^2 x - 7cos x + 2 = 0
-2cos^2 - 7cos x + 4 = 0
D=49+32=81
cosx=1/2
x=+-п/3 + 2пn
2) cosx*(cosx+sinx)=0
cosx=0
x=п/2+пn
cosx+sinx=0
tgx=-1
x=п/4+пn
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Answers & Comments
1) 2-2cos^2 x - 7cos x + 2 = 0
-2cos^2 - 7cos x + 4 = 0
D=49+32=81
cosx=1/2
x=+-п/3 + 2пn
2) cosx*(cosx+sinx)=0
cosx=0
x=п/2+пn
cosx+sinx=0
tgx=-1
x=п/4+пn