a monic cubic polynomial px satisfied the condition p(1). p(3) =17. p(5). find p(2) ..
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Answer :
we know that general form of a cubic polynomial is p(x) = ax³ + bx² + cx + d
given that p(1) = 1
⇒ p(1) = a + b + c + d = 1
p(2) = 2
⇒ p(2) = 8a + 4b + 2c + d = 2 and since a + b + c + d = 1
⇒ 7a + 3b + c = 1
p(3) = 3
⇒ 27a + 9b + 3c + d = 3
since a + b + c + d = 1
⇒ 26a + 8b + 2c = 2
since 7a + 3b + c = 1 and 14a + 6b + 2c = 2
⇒ 12a + 2b = 0
⇒ 6a + b = 0 ⇒ b = -6a
substituting b = -6a in 7a + 3b + c = 1
we get -11a + c = 1
p(4) = 5
⇒ 64a + 16b + 4c + d = 5
since a + b + c + d = 1
⇒ 63a + 15b + 3c = 4
substituting b = -6a in 63a + 15b + 3c = 4 we get
63a - 90a + 3c = 4 ⇒ -27a + 3c = 4
solving equations -11a + c = 1 and -27a + 3c = 4
we get a = 1/6 and c = 17/6 and b = -6a = -1
substituting all the values in a + b + c + d = 1 we get d = -1
so the given polynomial is x³/6 - x² + 17x/6 - 1
⇒ p(6) = 6² - 6² + 17 - 1 = 16
Answer:
we know that general form of a cubic polynomial is p(x) = ax³ + bx² + cx + d
given that p(1) = 1
⇒ p(1) = a + b + c + d = 1
p(2) = 2
⇒ p(2) = 8a + 4b + 2c + d = 2 and since a + b + c + d = 1
⇒ 7a + 3b + c = 1
p(3) = 3
⇒ 27a + 9b + 3c + d = 3
since a + b + c + d = 1
⇒ 26a + 8b + 2c = 2
since 7a + 3b + c = 1 and 14a + 6b + 2c = 2
⇒ 12a + 2b = 0
⇒ 6a + b = 0 ⇒ b = -6a
substituting b = -6a in 7a + 3b + c = 1
we get -11a + c = 1
p(4) = 5
⇒ 64a + 16b + 4c + d = 5
since a + b + c + d = 1
⇒ 63a + 15b + 3c = 4
substituting b = -6a in 63a + 15b + 3c = 4 we get
63a - 90a + 3c = 4 ⇒ -27a + 3c = 4
solving equations -11a + c = 1 and -27a + 3c = 4
we get a = 1/6 and c = 17/6 and b = -6a = -1
substituting all the values in a + b + c + d = 1 we get d = -1
so the given polynomial is x³/6 - x² + 17x/6 - 1
⇒ p(6) = 6² - 6² + 17 - 1 = 16