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Let P(x) be quadratic polynomical with r...

Let `P(x)` be quadratic polynomical with real coefficient such tht for all real `x(1)` the relation `2(1 + P(x)) = P(x - 1) + P(x + 1)` holds. If `P(0) = 8` and `P(2) = 32` then
If the range of `P(x)` is `[m, oo)` then `'m'` is less then

A

`-12`

B

15

C

`-17`

D

`-5`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will start with the given conditions and work through the quadratic polynomial. ### Step 1: Define the Quadratic Polynomial Let \( P(x) = ax^2 + bx + c \). ### Step 2: Use the Given Condition \( P(0) = 8 \) Substituting \( x = 0 \): \[ P(0) = a(0)^2 + b(0) + c = c = 8 \] Thus, we have: \[ c = 8 \] ### Step 3: Use the Given Condition \( P(2) = 32 \) Substituting \( x = 2 \): \[ P(2) = a(2)^2 + b(2) + c = 32 \] Substituting \( c = 8 \): \[ 4a + 2b + 8 = 32 \] Simplifying this: \[ 4a + 2b = 32 - 8 = 24 \] Dividing the entire equation by 2: \[ 2a + b = 12 \quad \text{(Equation 1)} \] ### Step 4: Use the Given Relation The relation given is: \[ 2(1 + P(x)) = P(x - 1) + P(x + 1) \] Expanding both sides: - Left side: \[ 2(1 + P(x)) = 2 + 2P(x) = 2 + 2(ax^2 + bx + 8) = 2 + 2ax^2 + 2bx + 16 = 2ax^2 + 2bx + 18 \] - Right side: \[ P(x - 1) = a(x - 1)^2 + b(x - 1) + 8 = a(x^2 - 2x + 1) + b(x - 1) + 8 \] \[ = ax^2 - 2ax + a + bx - b + 8 = ax^2 + (-2a + b)x + (a - b + 8) \] \[ P(x + 1) = a(x + 1)^2 + b(x + 1) + 8 = a(x^2 + 2x + 1) + b(x + 1) + 8 \] \[ = ax^2 + 2ax + a + bx + b + 8 = ax^2 + (2a + b)x + (a + b + 8) \] Adding these: \[ P(x - 1) + P(x + 1) = [ax^2 + (-2a + b)x + (a - b + 8)] + [ax^2 + (2a + b)x + (a + b + 8)] \] \[ = 2ax^2 + (0)x + (2a + 16) \] ### Step 5: Set the Two Sides Equal Equating both sides: \[ 2ax^2 + 18 = 2ax^2 + 2a + 16 \] This simplifies to: \[ 18 = 2a + 16 \] Solving for \( a \): \[ 2a = 18 - 16 = 2 \implies a = 1 \] ### Step 6: Substitute \( a \) Back to Find \( b \) Using Equation 1: \[ 2(1) + b = 12 \implies 2 + b = 12 \implies b = 10 \] ### Step 7: Write the Polynomial Now we have: \[ P(x) = x^2 + 10x + 8 \] ### Step 8: Find the Range of \( P(x) \) To find the range of the quadratic polynomial, we can complete the square: \[ P(x) = (x^2 + 10x + 25) - 25 + 8 = (x + 5)^2 - 17 \] The vertex of this parabola is at \( (-5, -17) \). Since the parabola opens upwards, the minimum value of \( P(x) \) is \( -17 \). ### Conclusion The range of \( P(x) \) is \( [-17, \infty) \). Therefore, \( m = -17 \). ### Final Answer Since the question asks for \( m \) to be less than a certain value, we conclude: \[ m < -5 \]
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