Question

If the angles of a triangle ABC be in A.P., then

• A. c² = a² + b²– ab
• B. b² = a² + c² – ac
• C. a²= b² + c² – ac
• D. b² = a² + c²

Answer 1

Answer: (B)

b² = a² + c² – ac

Answer 2

Let the angle are a – d, a, a + d

\ a – d + a + a + d = 180⁰ ̃ a = 60⁰

\ ĐB = 60º, cos B = $\frac { \mathrm { c } ^ { 2 } + \mathrm { a } ^ { 2 } - \mathrm { b } ^ { 2 } } { 2 \mathrm { ca } }$

̃ $\frac { 1 } { 2 }$ = $\frac { \mathrm { c } ^ { 2 } + \mathrm { a } ^ { 2 } - \mathrm { b } ^ { 2 } } { 2 \mathrm { ca } }$ ̃ b² = a² + c² – ac