=2-5/12-5/18+1/12-7/18-42/17
=2-(5/12-1/12)-(5/18+7/18)-42/17
=2-4/12-12/18-42/17
=2-1/3-2/3-42/17
=2-1-42/17
=1-42/17
=-25/17
答案-1又17分之8