Question

If cos a + 2cos b + cos c = 2 then a, b, c are in

(A) 2b = a + c (B) b² = a × c (C) a = b = c (D) None of these​

Answer 1

Answer:

a 2

+b

2

+c

2

=2(a+2b−2c)−9

a

2

−2a+b

2

−4b+c

2

+4c+9=0

a

2

−2(a)(1)+(1)

2

+b

2

−2(b)(2)+(2)

2

+c

2

+2(c)(2)+(2)

2

=0

(a−1)

2

+(b−2)

2

+(c+2)

2

=0

⟹a=1,b=2,c=−2

a+b+c=1+2−2=1

Step-by-step explanation:

Hope this helps you