<span>6х^2+7=0
</span><span>6х^2= - 7
</span>х^2= - 7/6
т.к. - 7/6 <0 , следовательно , нет решения
ОТВЕТ:НЕТ РЕШЕНИЯ
2cos 165+75/2*cos165-75/2=2cos120*cos45=2 * (-1/2) * √2/2=-√2/2
Sin(-23π/4)*tg(19π/6)=sin(-22π/4-π/4)*tg(3π+π/6) = sin(π/4)*tg(π/6)=√2/2* 1/√3=√6/6