Question

己知y=y1+y2,y1与x成正比例,y2与x成反比例,并且x=1时,y=7;x=3时,y=13,求y与x的解析式,并求

Answer 1

y1=kx

y2=m/x

则y=kx+m/x

x=1

y=k+m=7

x=3

y=3k+m/3=13

解得k=4,m=3

所以y=4x+3/x

x=-1

y=-4-3=-7