If both (x - 2) and  are factors of px2 + 5x + r, show that p

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 Multiple Choice QuestionsShort Answer Type

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129. If both (x - 2) and open parentheses straight x minus 1 half close parentheses are factors of px2 + 5x + r, show that p = r.


Let f(x) = px2 + 5 x + r
If (x - 2) is a factor of f (x), then by factor theorem
f(2) = 0 | x - 2 = 0 ⇒ x = 2
⇒ p(2)2 + 5(2) + r = 0
⇒ 4p + r + 10 = 0    ...(1)

If open parentheses straight x minus 1 half close parentheses is a factor of f (x), then by factor theorem,

straight f open parentheses 1 half close parentheses equals 0 space space space space space space space space space space space space space space space space space space space space space space space space space vertical line space straight x minus 1 half equals 0 rightwards double arrow straight x equals 1 half space rightwards double arrow space straight x equals 1 half
rightwards double arrow space space space straight p open parentheses 1 half close parentheses squared plus 5 open parentheses 1 half close parentheses plus straight r equals 0
rightwards double arrow space space space space straight p over 4 plus 5 over 2 plus straight r equals 0
rightwards double arrow space space space straight p plus 4 straight r plus 10 equals 0 space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis

Subtracting (2) from (1), we get
3p - 3r = 0
⇒    p = r

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