18/u=15/(u-2)
u=(18u-36)/15
15u=18u-36
3u=36
u=12 км/ч- скорость лодки, принятая за u
Сокращаем на 7, a^2 и b
= 2/7ab
=(c^2-d^2)+(2c+2d)=(c-d)(c+d)+2(c+d)=(c+d)(c-d+2)
1. = с ^ ( ( 1/2 ) + ( 1/3 )) = с ^ ( 3/6 + 2/6 ) = с ^ 5/6
2. = y ^ ( - 1/3 + 1/4 ) = y ^ ( - 4/12 + 3/12 ) = y ^ ( - 1/12 ) = 1 / ( y ^12 )
3. = x ^ ( 2 + ( 1/2 )) = x ^ ( 5/2 )