скорость 1 рабочего=1/3
скорость 2 рабочего =1/5
20 мин=1/3 часа
первый оклеил 1/3 * 1/3=1/9 часть помещения
1-1/9=8/9 частей помещения осталось оклеить
скорость двух рабочих: 1/3 +1/5=8/15
8/9 :8/15= 15/9=5/3 часа=1ч+2/3ч=1ч40мин
1ч 40 мин +20 мин=2ч
ответ: помещение было оклеено за 2 часа
<span>1/2 log7 36 - log7 14 - 3log7 ∛21 = <span>1/2 log7 6² - <span>log7 14 - log7 (∛21)³ = </span></span></span>
<span><span><span>= 1/2 · 2· <span><span>log7 6 - <span><span><span>log7 14 - log7 21 = <span><span><span><span><span>log7 6 - <span><span><span>log7 14 - log7 21</span></span></span></span></span></span></span></span> = </span></span></span></span></span></span></span></span>
<span><span><span>= <span><span><span><span><span><span><span><span><span><span><span><span><span>log7 (6:14:21) = <span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span>lo</span></span></span></span></span></span></span></span>g7 (1/49) =<span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span> <span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span>lo</span></span></span></span></span></span></span></span>g7 (7⁻²) = -2<span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span><span>lo</span></span></span></span></span></span></span></span>g7</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span> 7 = -2·1 = -2</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
</span></span></span>
1)12:6*4=2*4=8(см)-длина отрезка ВС.