Given points are P(1,-1,5) , Q(5,6,1)

Let a=i-j+5k

b=PQ=(5-1)i+(6+1)j+(1-5)k=4i+7j-4k

The parametric equation of line segment PQ is r(t)=a+tb

r(t)=i-j+5k+t(4i+7j-4k)

r(t)=(1+4t)i+(7t-1)j+(5-4t)k

Where , x=1+4t

y=7t-1

z=5-4t

Let a=i-j+5k

b=PQ=(5-1)i+(6+1)j+(1-5)k=4i+7j-4k

The parametric equation of line segment PQ is r(t)=a+tb

r(t)=i-j+5k+t(4i+7j-4k)

r(t)=(1+4t)i+(7t-1)j+(5-4t)k

Where , x=1+4t

y=7t-1

z=5-4t