Trong tam giacsbABC thỏa các đẳng thức sau. Tìm các hệ số a;b;c
1) sinA + sinB + sinC = a+bcosA/2.cosB/2.cosC/2.
2) sin4A+sin4B+sin4C = a+bsin2A.sin2B.sin2C.
3) cos4A+cos4B+cos4c = a+bcos2A.cos2B.cos2C.
4) cos2A +cos2B+cos2C = a+bcosA.cosB.cosC
VIẾT LẠI CÂU CÓ NGHĨA KHÔNG ĐỔI:
1. We couldn't drive because of the fog.
- The fog was .................................
2. The postman was bitten by dog.
- The dog........................................
3. The cake was so hard that I couldn't.
- It was..............................
4.Although his leg was broken, he managed to get out of the car.
-In spite of.............................
5.We didn't go because it rainned
-If...................................................