Найдите значении выражения x-y^2(x+y) при x= -1 1/2 (дробь) y=2/3 (дробь)

Х - y^2•( X + y )
X = - 1 ( 1/2 )
y = 2/3
Решение
1) - 1 ( 1/2 ) + ( 2/3 ) = - 1 ( 3/6 ) + ( 4/6 ) = - ( 9/6 ) + ( 4/6 ) = - 5/6
2) ( 2/3)^2 •( - 5/6 ) = 4/9 • ( - 5/6 ) = - 20/54 = - 10/27
3) - 1 ( 1/2 ) - ( - 10/27 ) = - 1 ( 27/54 ) + ( 20/54 ) = - 1 ( 7/54 )
ответ ( - 1 ( 7/54 ))

-1(1/2)+(2/3)=-1(3/6)+(4/6)=-(9/6)+(4/6)=-5/6 
(2/3)^2*(-5/6)=4/9*(-5/6)=-20/54=-10/27 
-1(1/2)-(-10/27)=-1(27/54)+(20/54)=-1(7/54) 
ответ:-1(7/54)