a) You can use 3 different numbers for t. How about 5, 10, 20?
.. [x, y] = [2, -3] +5[5, 1] = [27, 2]
.. [x, y] = [2, -3] +10[5, 1] = [52, 7]
.. [x, y] = [2, -3] +20[5, 1] = [102, 17]
b) You can replace t with any function of whatever parametric variable you want to use. For example, t = -3s+2.
.. [x, y] = [2, -3] +(-3s +2)[5, 1]
.. = [2 -15s +10, -3 -3s +2]
.. [x, y] = [12, -1] +s[-15, -3]
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The graph uses "t" instead of "s" for the parameter of the second version of the line. This is a Desmos thing: it likes "t" for parametric equations. The second equation is shown as dotted, so you can see it is the same line as the first equation (solid red).
