if,a2,b2,c2 are in AP, then which of the following is also in AP ?

∵a2,b2,c2 are in AP.⇒ sin2 ⁡B−sin2 ⁡A=sin2 ⁡C−sin2 ⁡B⇒ sin ⁡C(sin⁡ Bcos ⁡A−cos ⁡Bsin ⁡A)=sin⁡ A(sin ⁡Ccos ⁡B−cos⁡ Csin ⁡B)On dividing by sin Asin B sin C, we get2cot ⁡B=cot ⁡A+cot⁡ C⇒ cot⁡A,cot⁡B,cot⁡C are in AP.