Eliminate t to give an equation that relates x and y:
x=tan(t), y=sec^2(t)-4
x=tan(t), y=sec^2(t)-4
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sec^2(t) = 1 + tan^2(t) (pythagoras identity)
so, sec^2(t) = 1 + x^2
==> y = 1 + x^2 - 4
==> y = x^2 - 3
so, sec^2(t) = 1 + x^2
==> y = 1 + x^2 - 4
==> y = x^2 - 3