Question

已知y=y1+y2,y1与x的平方成正比例,y2与x成反比例,并且当x=1时,y=1,当x=3时,求x=-1时,y的值.

Answer 1

y1与x的平方成正比例,y1=mx^2

y2与x成反比例,y2=n/x

y=y1+y2 = mx^2+n/x

x=1时,y=1,m+n=1

x=3时,y=-17,9m+n/3=-17

m=-2,n=3

x=-1时,y= mx^2+n/x = m-n = -2-3 = -5