<span> 5y-x=6
</span><span>3x-4y=4
--------------
х=5у-6
3х-4у=4
--------------
</span><span>х=5у-6
3(5у-6)-4у=4
--------------
</span><span>х=5у-6
15у-18-4у=4
----------------
</span><span>х=5у-6
11у=22
-----------------
х=5у-6
у=2
--------------
х=5·2-6
у=2
------------
х=4
у=2
</span>
<span>Sin 5п/6 - sin п/6=sin(π-π/6)-sinππ/6=sinπ/6-sinπ/6=0
-cos 2п/3 - (- cos п/3)=-cos(π-π/3)+cosπ/3=cosπ/3+cosπ/3=1/2+1/2=1</span>