1.Составить во к следующим ответам.
1. I am doing my homework now.
2. They usually do their homework in the evening
3. My mother went shopping last Friday.
4. My friends have been in Italy 2 years ago.
2. Используйте глаголы в скобках в правильной форме.
1. I (has written, wrote, have written)
the letter yesterday.
2. Tamara (has, have) already (cleans, cleaned) the room.
3. I (have done, is doing, am doing) my lessons now.
4. He (has done, have done, did) his exercises till six o’clock.
Объяснение:
1.Составить во к следующим ответам.
1. I am doing my homework now.
2. They usually do their homework in the evening
3. My mother went shopping last Friday.
4. My friends have been in Italy 2 years ago.
2. Используйте глаголы в скобках в правильной форме.
1. I (has written, wrote, have written)
the letter yesterday.
2. Tamara (has, have) already (cleans, cleaned) the room.
3. I (have done, is doing, am doing) my lessons now.
4. He (has done, have done, did) his exercises till six o’clock.
Найдём tgα
2tg²α + 5tgα + 2 = 0 - уравнение квадратное относительно tgα.
D = b²- 4ac = 25 - 16 = 9; √D = 3.
tgα = (-5 + 3)/4 = 0,5 - не удовлетворяет условие \frac{3\pi}{4} \ \textless \ \alpha \ \textless \ \pi
или tgα = (-5 - 3)/4 = -2.
Найдём tg2α:
tg2α = (2tgα)/(1 - tg²α) = -4/(1 - 4) = 4/3 где (3π/2) < 2α < 2π.
Рассмотрим 4 и 3 как противолежащий и прилегающий катеты прямоугольного треугольника, с гипотенузой 5 (Египетский треугольник). Тогда, с учётом условия (3π/2) < 2α < 2π, cos2α = 3/5 = 0,6.
ответ: 0,6.
