(5+6)/5*6 -(6+7)/6*7+(7+8)/7*8-(8+9)/8*9
=5/5*6+6/5*6-(6+7)/6*7+(7+8)/7*8-(8+9)/8*9
=1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9
=1/5-1/9
=4/45
5x6分之5+6减6x7分之6+7加7x8分之7+8减8x9分之8+9等于
(5+6)/5*6 -(6+7)/6*7+(7+8)/7*8-(8+9)/8*9
=5/5*6+6/5*6-(6+7)/6*7+(7+8)/7*8-(8+9)/8*9
=1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9
=1/5-1/9
=4/45