设a(5,-3),b(-2,9),求a+b,-2a,4a-5b 的坐标.
问题描述:
设a(5,-3),b(-2,9),求a+b,-2a,4a-5b 的坐标.
答
a+b=(5,-3)+(-2,9)=(3,6),
-2a=-2(5,-3)=(-10,6),
4a-5b =4(5,-3)-5(-2,9)
=(20,-12)-(-10,45)=(30,-57).