Q31 In a triangle ABC, if
1 1 1 1+cosA 1+cosB 1+cosC cosA+cos2A cosB+cos2B cosC+cos2C
=0,then prove that ABC is an isosceles triangle
Solution
,
| 1 | 1 | 1 |
| 1+cosA | 1+cosB | 1+cosC |
| cosA+cos2A | cosB+cos2B | cosC+cos2C |