Question

If roots of equation x³ – 12x² + 39x – 28 = 0 are in A.P. then common difference =

• A. ±1
• B. ±2
• C. ±3
• D. ±4

Answer 1

Answer: (C)

±3

Answer 2

Let a – d, a, a + d be roots

a – d + a + a + d = (–1)¹ ⋅ $\frac { ( - 12 ) } { 1 }$

3a = 12 ̃ a = 4

(4 – d) (4) (4 + d) = (–1)³. $\frac { ( - 28 ) } { 1 }$

16 – d² = 7 ̃ d² = 9 ̃ d = ± 3