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If one of the roots of the equation x2 - bx + c = 0 is the square of the other, then which of the following option is correct ?
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- b3 = 3bc + c2 + c
- c3 = 3bc + b2 + b
- 3bc = c3 + b2 + b
- 3bc = c3 + b3 + b2
Correct Option: A
Given that, one root of the equation
x2 - bx + c = 0 is square of other root of this equation i.e., roots (α, α2).
∴ Sum of roots = α + α2 = -(-b)/1
⇒ α (α + 1) = b .......(i)
and product of roots= α. α2 = c/1
⇒ α3 = c ⇒ = c1/3 ....(ii)
From Eqs. (i) and (ii).
c1/3 (c1/3 + 1) = b ....(iii)
On cubing both sides, we get
c(c1/3 + 1)3 = b3
⇒ c {c + 1 + 3c1/3 (c1/3 + 1)} = b3
⇒ c {c + 1 = 3b} = b3 [from Eq. (iii)]
⇒ b3 = 3bc + c2 + c