2/1÷3÷4/3
=2/1×1/3×3/4
=2/1×(1/3×3/4)
=2×1/4
=1/2
1÷3/7×9/28×4/3
=1×7/3×9/28×4/3
=1×(7/3×4/3)×9/28
=1×28/9×9/28
=1×(28/9×9/28)
=1×1
=1
2/1÷3÷4/3
=2/1×1/3×3/4
=2/1×(1/3×3/4)
=2×1/4
=1/2
1÷3/7×9/28×4/3
=1×7/3×9/28×4/3
=1×(7/3×4/3)×9/28
=1×28/9×9/28
=1×(28/9×9/28)
=1×1
=1