Question 1038703
For {{{t<=1}}}, only the first tractor is moving.
{{{D[1]}}}=({{{0}}},{{{20t}}})
{{{D[2]}}}=({{{0}}},{{{0}}})
{{{D[1-2]}}}=({{{0}}},{{{20t}}}
{{{abs(D[1-2])=20t}}}({{{0<=t<=1}}})
For {{{t>1}}}, both tractors are moving perpendicularly to each other,
tractor 1 is already 20 miles north of the starting point,
{{{D[1]}}}=({{{0}}},{{{20t}}})
{{{D[2]}}}=({{{-35(t-1)}}},{{{0}}})
{{{D[1-2]}}}=({{{35(t-1)}}},{{{20t}}})
{{{abs(D[1-2])=sqrt((35(t-1))^2+(20t)^2)}}}
{{{abs(D[1-2])=sqrt(1225t^2-2450t+1225+400t^2)}}}
{{{abs(D[1-2])=sqrt(1625t^2-2450t+1225)}}}({{{t>1}}})
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I used {{{t}}} as the time variable instead of {{{x}}}.