Metamath Proof Explorer


Theorem acoscosb

Description: Relationship between cosine and arccosine. (Contributed by Mario Carneiro, 2-Apr-2015)

Ref Expression
Assertion acoscosb ABB0πarccosA=BcosB=A

Proof

Step Hyp Ref Expression
1 cosacos AcosarccosA=A
2 1 3ad2ant1 ABB0πcosarccosA=A
3 fveqeq2 arccosA=BcosarccosA=AcosB=A
4 2 3 syl5ibcom ABB0πarccosA=BcosB=A
5 acoscos BB0πarccoscosB=B
6 5 3adant1 ABB0πarccoscosB=B
7 fveqeq2 cosB=AarccoscosB=BarccosA=B
8 6 7 syl5ibcom ABB0πcosB=AarccosA=B
9 4 8 impbid ABB0πarccosA=BcosB=A