найдите наименьшее и наибольшее значение функции f(x)=2x^3+3x+2 на промежутке [-2;1]

Раскройте скобки, употребите глаголы, данные в скобках, в нужной форме: 1 ) He ( to return) to Moscow two days ago. 2) The train (to arrive) at 5 o’clock tomorrow. 3) My sister plays tennis but she ( to prefer) to play basketball. 4) This week we (to take) part in a conference. 5) All the events (to go) on long ago. 6) Summer session (to begin) next week. 7¬) They ( to read) the newspaper every day 8) He always (to prepare) his homework carefully. 9) She (to speak) several foreign languages. 10) The children (to play) in the park every afternoon. 11) They always ( to travel) by car. 12) He ( to know) French very good next year. 13) She (to make) mistakes in spelling yesterday. 14) She always (to come) to lectures late. 15) He (to arrive) home tomorrow. 16) They (to work) in our garden yesterday. 17 ) He (to want) to learn English. 18) They (to talk) over the telephone yesterday. 19) She (to study) in our group last semester.

Раздел математики 9 букв, первая г

постройте сечение тетраэдара ABCD плоскостью, проходящей через точку M принадлежащей DA, N пренадлежащей DC, K принадлежащей BC

cos7xcos13x=cosxcos19x

если честно я и формулу знаю какую приминить,только вот одно не помню...куда деть (1./2-ые?)
 вот застряла)))))))))))
1/2(cos(7x+13x)+cos(7x-13x)=1/2(cos(x+19x)+cos(x-19x)=

1/2(cos20x+cos6x)-1/2(cos20x+cos18x)=0
Можно сокращать/.??