Đáp án:
`A=-7/5`
Giải thích các bước giải:
`A=1/13+(-5/18-1/13+12/17)-(12/17-5/18+7/5)`
`A=1/13-5/18-1/13+12/17-12/17+5/18-7/5`
`A=1/13-1/13-5/18+5/18+12/17-12/17-7/5`
`A=(1/13-1/13)-(5/18-5/18)+(12/17-12/17)-7/5`
`A=0-0+0-7/5`
`A=0+0-7/5`
`A=0-7/5`
`A=-7/5`