Sin = -12/13
ctg=cos/sin= -(5/13)/(12/13)=-5/12
Решение смотри в приложении
<span>18-3x</span>² <span>= 0
-3х</span>² = -18
<span>
х</span>² = -18/-3
<span>
х</span>² = 6
<span>
х = +- </span>√6
<span>
х1 = -</span>√6
<span>х2 = </span>√6<span>
</span>