(2倍a的2/3次方倍b的1/2被)(-6倍a的1/2次方倍b的1/3次方）除以（-3倍a的1/6次方b的5/6次方）
=2a^(2/3)b^(1/2)(-6a^(1/2)b^(1/3）/(-3a^(1/6)b^(5/6))
=4a^(2/3+1/2-1/6)b^(1/2+1/3-5/6)
=4a^(6/6)b^0
=4a