Продолжите фразы 1) система...2) системный подход... 3) структура... 4) системный эффект...

 Correct the following sentences putting the verb into negative form

1 To play football you need a racket and a ball

2 A cyclist drives a car

3 A swimmer swims on a count

4 They play basketball in a swimming pool

5  A tennis plays tennis alone

6 A volleyball player kicks the ball

7   They play hockey in the water

8 A boxer fights two people

в одной пачке 10 книг.на сколько книг меньше в 4 таких пачках,чем в 7 таких пачках.

Пожалуста помогите решить a^2-x^2 при  a=4.5,x=2.5