问题补充:
答案:
cos(A-B)cosB-sin(A-B)sin(A+C)=-3/5 ∵A+C=180-B ∴sin(A+C)=sinB ∴cos(A-B)cosB-sin(A-B)sinB=-3/5 ∴cos(A-B+B)=-3/5 即cosA=-3/5
时间:2024-08-04 09:15:03
cos(A-B)cosB-sin(A-B)sin(A+C)=-3/5 ∵A+C=180-B ∴sin(A+C)=sinB ∴cos(A-B)cosB-sin(A-B)sinB=-3/5 ∴cos(A-B+B)=-3/5 即cosA=-3/5
在△ABC中 内角A B C所对应的边分别a b c 若c²=(a-b)²+6
2020-03-29