−15, 41⋅(−3, 5) (У першому віконці пиши знак +, якщо результат додатний, і знак −, якщо результат від'ємний)

a little monkey was sitting on a tree. she was bored and she wanted to eat. she got down the tree and looked through the jungle to find a banana of a mango. but there was no fruits and even no tasty leafs. she was upset. she wandered through the jungle and meet her friends - green crocodile and bright parrot. parrot was very hungry too because he also couldn't find anything to eat. they decided to walk together. in a minute they noticed a huge yelow banana lying on the floor. monkey clutched it and at once many hunters with guns run to the glade.

friends started to run away. they ran through the bush and high grass and they saved their lives from the crafty hunters

ответ:   26 км/час.

Пошаговое объяснение:

Решение.

x км/час --- собственная скорость лодки.

x-4 км/час ---   скорость лодки против течения.

x+4 км/час ---   скорость лодки по течению.

165 км - расстояние пройденное лодкой.

t1=165/(x-4) - время затраченное на передвижение против течения.

t2=165/(x+4) - время затраченное на передвижение по течению.

По условию задачи t1-t2=2 часа:

165/(x-4) - 165/(x+4) = 2;

165(x+4) - 165(x-4) = 2(x+4)(x-4);

165x + 660-165x+660 = 2x² - 32;

2x² - 32 - 1320=0;

2x² = 1352;

x² =676;

x1=26;  x2=-26 - не соответствует условию.

x=26 км/час --- собственная скорость лодки.