t= 0.00
01
} start & end points r0=3,2,4,
r1=2,4,1


r(t)=(1t)r0+tr1,0t1
You can think of t as giving a percentage, namely the percentage r(t) has moved away from r0 and towards r1.
When t= 0.00, r(t) is 100% towards r0 and 0% towards r1.