[17/4一(2/7 13/42)]÷13/4
=[17/4一(2/(307/42))]×4/13
=17/4×4/13一(2/(307/42))×4/13
=17/13-84/307×4/13
=(17-336/307)/13
=(4883/307)/13
=4883/3991
=1又892/3991
【17/4-(2/7+13/42)】÷13/4
=【17/4-(12/42+13/42)】÷13/4
=【17/4-25/42】÷13/4
=17/4×4/13-25/42×4/13
=17/13-50/273
=357/273-50/273
=307/273
=1又34/273