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-0,6х+0,8=1-х-0,5
0,4х=-0,3
<em>х=-3/4 (а)</em>
(1+sina)(sina-1)=(sina+1)(sina-1)=sin²a-1=-(1-sin²a)=-cos²a
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Cos²A=1-sin²A=1-(-2√6/5)=1-24/25=1/25
cosA=√1/25=1/5