Question

英语好的 数学好的帮忙 解下这道题 很急 速度 谢谢

airports A and B are such that AB=(600i+200j)km.an aircraft is to be flown directly from A to B.the aircraft can maintain a steady speed of 390km\h in still air. there is a wind blowing with velocity (30i-20j)km\h.find,in the form ai+bj,the velocity vector the pilot should set so that this velocity. together with the wind, causes the plane to travel directly from A to B

Answer 1

(30i-20j)+(ai+bj)=(30+a)i+(b-20)j
(30+a)/(b-20)=600/200=3
a=3b-90
显然b-20>0,b>20

而a^2+b^2=390^2
(3b-90)^2+b^2=390^2
b^2-54b-96*150=0
(b-150)(b+96)=0
b=150或b=-96(舍弃)

所以：a=3*150-90=360
所以：ai+bj=360i+150j