来自马小强的问题
已知△ABC的内角A,B,C成等差数列,则cos2A+cos2C的取值范围是___.
已知△ABC的内角A,B,C成等差数列,则cos2A+cos2C的取值范围是___.
1回答
2020-04-05 21:30
已知△ABC的内角A,B,C成等差数列,则cos2A+cos2C的取值范围是___.
已知△ABC的内角A,B,C成等差数列,则cos2A+cos2C的取值范围是___.
∵A,B,C成等差数列,
∴2B=A+C,又A+B+C=π,
∴B=60°,即A+C=120°,
cos2A+cos2C
=1+cos2A2