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acoldgirl


Chứng minh hộ mình các câu sau nhé! Thank you chiu chiu!!!!!!!!!
1. cosA+cosB+cosC = 1+4sin(A/2)sin(B/2)sin(C/2)
2. cotA.cotB + cotB.cotC + cotC.cotA = 1
3. tan(A/2).tan(B/2) + tan(B/2).tan(C/2) + tan(C/2).tan(A/2) = 1
4. cot(A/2)+cot(B/2)+cot(C/2) = cot(A/2).cot(B/2).cot(C/2)
Giúp mình với nhé!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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1. cosA+cosB+cosC = 1+4sin(A/2)sin(B/2)sin(C/2)
2. cotA.cotB + cotB.cotC + cotC.cotA = 1
3. tan(A/2).tan(B/2) + tan(B/2).tan(C/2) + tan(C/2).tan(A/2) = 1
4. cot(A/2)+cot(B/2)+cot(C/2) = cot(A/2).cot(B/2).cot(C/2)
Giúp mình với nhé!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!