Theorem neg1sqe1

Description: The square of -u 1 is 1. (Contributed by David A. Wheeler, 8-Dec-2018)

	Ref	Expression
Assertion	neg1sqe1	$$⊢{\left(-1\right)}^2=1$$

Proof

Step	Hyp	Ref	Expression
1		ax-1cn	$$⊢1\in ℂ$$
2		sqneg	$$⊢1\in ℂ\to {\left(-1\right)}^2=1^2$$
3	1 2	ax-mp	$$⊢{\left(-1\right)}^2=1^2$$
4		sq1	$$⊢1^2=1$$
5	3 4	eqtri	$$⊢{\left(-1\right)}^2=1$$