Question

Sides of AABC are in A.P. If a < min {b,c} then cosA may be​

Answer 1

Answer:

∵Sides are in A.P and a<min{b,c}

CaseI:If min{b,c}=b

⇒a,b,c are in A.P.

⇒2b=a+c

⇒a=2b−c

∴cosA=2bcb2+c2−a2        

       =2bcb2+c2−(2b−c)2

      =2bcb2+c2−4b2−c2+4bc

      =2bc−3b2+4bc

     =2bcb(4c−3b)=2c4c−3b

CaseII:If min{b,c}=c

⇒2c=a+b

⇒a=2c−b

∴cosA=2bc