... α ( t ) p 2 ( t ) , α ( t ) p3 ( t ) + α ( t ) p3 ( t ) =α ( t ) p1 ( t ) , α ( t ) p 2 ( t ) , α ( t ) p3 ( t ) +α ( t ) p1 ( t ) , α ( t ) p 2 ( t ) , α ( t ) p3 ( t ) = ... p 2 ( t ) , p3 ( t )) ,−→q ( t ) = ( q1 ( t ) , q 2 ( t ) , q3 ( t )) , khi đó:ddt−→p ( t ) +−→q ( t ) =ddt ( p1 ( t ) + q1 ( t ) , p 2 ( t ) + q 2 ( t ) , p3 ( t ) + q3 ( t )) =p1 ( t ) + ... q3 ( t ) =d−→p ( t ) dt+d−→q ( t ) dtb.ddtα ( t ) −→p ( t ) =[α ( t ) p1 ( t )] ,[α ( t ) p 2 ( t )] ,[α ( t ) p3 ( t )] =α ( t ) p1 ( t ) + α ( t ) p1 ( t ) , α ( t ) p 2 ( t ) +...