упростите выражение xy-7x-(x-4xy)

Правильны ли определение , которыми пользовался учитель 

а)корень - это неизменяемая часть речи однокоренных слов .

б)окончание - это изменяемая часть , которая стоит на конце слова.

докажите свою точку зрения.

arctg(- √3/3 ) - π/3 = что получится? срочно!!!!

Помогите пожалуйста написать сочинение по экономике 6 класс  со словами: потребитель,рынок,бартер, продавец,покупатель,ресурсы,спрос,предложение,конкуренция.

Раскройте скобки, употребляя глаголы в Present или Past Indefinite. Помогите, пожалуйста. 1. I (to go) to bed at 10 o'clock every day. 2. I (to go) to bed at 10 o'clock yesterday. 3. My brother (to wash) his face every morning. 4. Yesterday he (to wash) his face at a quarter past seven. 5. I (not to have) History lessons every day. 6. We (not to rest) yesterday. 7. My brother (not to drink) coffee yesterday. 8. My mother always (to take) a bus to get to work, but yesterday she (not to take) a bus. Yesterday she (to walk) to her office. 9. You (to talk) to the members of your family every day? - Yes, I ... . But yesterday I (not to talk) to them: I (to be) very busy yesterday. 10. You (to come) home at 6 o'clock yesterday? - No, I ... . Yesterday I (to come) home from school at half past eight. I (to be) very tired. I (to have) dinner with my family. After dinner I (to be) very thirsty. I (to drink) two cups of tea. Then I (to rest). 11. Your sister (to go) to school every day? - Yes, she ... .