(2a的平方+ab-2b的平方)×(-1/2ab)
=2a的平方×(-1/2ab) +ab×(-1/2ab) -2b的平方 ×(-1/2ab)
=-a³b-1/2a²b²+ab³
(2x+3y)(4x+7y)
=8x²+14xy+12xy+21y²
=8x²+26xy+21y²
(a+9)(a+1)
=a²+a+9a+9
=a²+10a+9
(2a的平方+ab-2b的平方)×(-1/2ab)
=2a的平方×(-1/2ab) +ab×(-1/2ab) -2b的平方 ×(-1/2ab)
=-a³b-1/2a²b²+ab³
(2x+3y)(4x+7y)
=8x²+14xy+12xy+21y²
=8x²+26xy+21y²
(a+9)(a+1)
=a²+a+9a+9
=a²+10a+9