Question

3、已知x分之1+y分之1=5,求x-2xy+y分之2x+3xy+2y的值

Answer 1

解

1/x+1/y=5

即(y+x)/xy=5

∴y+x=5xy

∴(2x+3xy+2y)/(x-2xy+y)

=[2(x+y)+3xy]/[(x+y)-2xy]

=[2×5xy+3xy]/(5xy-2xy)

=(13xy)/(3xy)

=13/3

x+4>0

x>-4

2x+5