Is there a rational number whose square is negative 9 Be specific

Is there a rational number whose square is negative 9 Be specific

The squares of rational numbers are all positive numbers, so there is no square. If the square is negative nine, it is an imaginary number, not a real number, let alone a rational number

Limit of limx (cubic) LNX when x tends to zero

Let x = 1 / T
The original limit is
lim(t->∞)(1/t^3)ln(1/t)
=LIM (T - > ∞) - LNT / T ^ 3 ∞ / ∞, using the law of Robita
=lim(t->∞)-1/t/3t^2
=0
So the original limit is 0

The process of LIM approaching to the equivalence proof of 0,1-cosx and (1 / 2) * (x ^ 2)