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$�� 79. �� :1) {x-y=?/3, cos^2(x)-cos^2(y)=-3/4};2) {x-y=?/3, cos(x)cos(y)=1/2};3) {x+y=1/3, sin(?x)+sin(?y)=1};4) {x+y=?/3,...$

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79. �� :

1) {x-y=?/3, cos^2(x)-cos^2(y)=-3/4};

2) {x-y=?/3, cos(x)cos(y)=1/2};

3) {x+y=1/3, sin(?x)+sin(?y)=1};

4) {x+y=?/3, sin(x)sin(y)=0,25}.

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