Прочитайте приведённые ниже предложения. Выберите и запишите
правильное слово. 1.Have you ever been to Australia? - Yes, I
(have/ had). We (sailed/ have sailed) there last September. 2. Have you written Exercise 4? - Yes. We (have done/ did) it at home yesterday.
3. I have explained the rule to Greg. I (have spoken/ spoke) to him after classes.
4. Mary (has received/ received) this task two days ago. I don't know if she (has already done/
already did) it. 5. (Have you rung/ Did you ring) the office manager yet? - Yes. I (have informed/
informed) her of your visit next week. 6. I (have done/ did) everything. Now I (am/ was) free and (can/ could) home. - Are you sure you (have done/ did) everything? 7.We first (saw/ have seen) this film five years
ago. 8. Has he handed in the project? - Yes, he has.
He (did/ has done) it last week.
9. Mother (gave/ has given) me some money. I can buy a new dictionary. 10. Helen (never swam/ has never swum) in the ocean
Прочитайте приведённые ниже предложения. Выберите и запишите
правильное слово. 1.Have you ever been to Australia? - Yes, I
(have/ had). We (sailed/ have sailed) there last September. 2. Have you written Exercise 4? - Yes. We (have done/ did) it at home yesterday.
3. I have explained the rule to Greg. I (have spoken/ spoke) to him after classes.
4. Mary (has received/ received) this task two days ago. I don't know if she (has already done/
already did) it. 5. (Have you rung/ Did you ring) the office manager yet? - Yes. I (have informed/
informed) her of your visit next week. 6. I (have done/ did) everything. Now I (am/ was) free and (can/ could) home. - Are you sure you (have done/ did) everything? 7.We first (saw/ have seen) this film five years
ago. 8. Has he handed in the project? - Yes, he has.
He (did/ has done) it last week.
9. Mother (gave/ has given) me some money. I can buy a new dictionary. 10. Helen (never swam/ has never swum) in the ocean
x = 1, y=5 или x=5, y=1
Пошаговое объяснение:
Заменяешь x+y на t.
t^2-7t+6=0
t+xy=11.
Решаешь первое уравнение через дискриминант или теорему Виета.
Корни получаются 6 и 1. Это значения x+y. Рассмотрим сначала первый вариант, когда x+y=6.
t=6
t+xy=11.
xy=5. Выразим из x+y=6 любую переменную, например x. x=6-y.
Подставим в xy=5.
(6-y)y=5
6y-y^2=5
y^2-6y+5=0
Находишь корни через дискриминант или теорему Виета уже для этого случая.
Корни получаются: 1;5
При y=1 x=5 и при y=5 x=1.
Рассмотрим второй случай, когда x+y=1 (Оно же t=1).
Подставим в t+xy=11.
xy=10
Выразим любую переменную.
x=1-y
(1-y)y=10
y-y^2=10
y^2-y+10=0
У этого выражения нет корней, т.к. дискриминант отрицательный, следовательно ответом будет (1;5),(5;1)