Definition df-cos 11661

Description: Define the cosine function. (Contributed by NM, 14-Mar-2005.)

Assertion

Ref	Expression
df-cos	|- cos = ( x e. CC |-> ( ( ( exp ` ( _i x. x ) ) + ( exp ` ( -u _i x. x ) ) ) / 2 ) )

Detailed syntax breakdown of Definition df-cos

Step	Hyp	Ref	Expression
1		ccos 11655	. 2 class cos
2		vx	. . 3 setvar x
3		cc 7811	. . 3 class CC
4		ci 7815	. . . . . . 7 class _i
5	2	cv 1352	. . . . . . 7 class x
6		cmul 7818	. . . . . . 7 class x.
7	4, 5, 6	co 5877	. . . . . 6 class ( _i x. x )
8		ce 11652	. . . . . 6 class exp
9	7, 8	cfv 5218	. . . . 5 class ( exp ` ( _i x. x ) )
10	4	cneg 8131	. . . . . . 7 class -u _i
11	10, 5, 6	co 5877	. . . . . 6 class ( -u _i x. x )
12	11, 8	cfv 5218	. . . . 5 class ( exp ` ( -u _i x. x ) )
13		caddc 7816	. . . . 5 class +
14	9, 12, 13	co 5877	. . . 4 class ( ( exp ` ( _i x. x ) ) + ( exp ` ( -u _i x. x ) ) )
15		c2 8972	. . . 4 class 2
16		cdiv 8631	. . . 4 class /
17	14, 15, 16	co 5877	. . 3 class ( ( ( exp ` ( _i x. x ) ) + ( exp ` ( -u _i x. x ) ) ) / 2 )
18	2, 3, 17	cmpt 4066	. 2 class ( x e. CC |-> ( ( ( exp ` ( _i x. x ) ) + ( exp ` ( -u _i x. x ) ) ) / 2 ) )
19	1, 18	wceq 1353	1 wff cos = ( x e. CC |-> ( ( ( exp ` ( _i x. x ) ) + ( exp ` ( -u _i x. x ) ) ) / 2 ) )

This definition is referenced by:  cosval  11713  cosf  11715  coscn  14230