Can 1-cost be replaced by 1-cost ~ x ^ 2 / 2 when Lim t tends to 0 T / radical? Why is there no limit

The answer upstairs is not correct
This problem is solved by lobida, which can never be solved, but must use half angle formula
If you do & nbsp; frac12; & nbsp; X & amp; sup2; & nbsp; & nbsp;, it's OK
The reason why limit does not exist is that left limit equals right limit, not substitution
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