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If one root of the equation 8x^(2) - 6x-...

If one root of the equation` 8x^(2) - 6x-a-3=0` is the square of the other values of a are :

A

`4,-24`

B

`4,24`

C

`-4,-24`

D

`-4,24`

Text Solution

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The correct Answer is:
To solve the quadratic equation \( 8x^2 - 6x - a - 3 = 0 \) given that one root is the square of the other, we can follow these steps: ### Step 1: Define the roots Let the roots of the equation be \( r \) and \( r^2 \), where \( r \) is one root and \( r^2 \) is the square of the other root. ### Step 2: Use Vieta's formulas According to Vieta's formulas for a quadratic equation \( ax^2 + bx + c = 0 \): - The sum of the roots \( r + r^2 = -\frac{b}{a} \) - The product of the roots \( r \cdot r^2 = \frac{c}{a} \) For our equation \( 8x^2 - 6x - (a + 3) = 0 \): - Here, \( a = 8 \), \( b = -6 \), and \( c = -(a + 3) \). ### Step 3: Set up the equations From Vieta's formulas: 1. \( r + r^2 = -\frac{-6}{8} = \frac{3}{4} \) (Sum of roots) 2. \( r \cdot r^2 = \frac{-(a + 3)}{8} \) (Product of roots) ### Step 4: Solve for \( r \) From the first equation, we can express \( r^2 \) in terms of \( r \): \[ r^2 + r - \frac{3}{4} = 0 \] This is a quadratic equation in \( r \). We can solve it using the quadratic formula: \[ r = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} = \frac{-1 \pm \sqrt{1^2 - 4 \cdot 1 \cdot \left(-\frac{3}{4}\right)}}{2 \cdot 1} \] \[ = \frac{-1 \pm \sqrt{1 + 3}}{2} = \frac{-1 \pm 2}{2} \] Thus, we have two possible values for \( r \): 1. \( r = \frac{1}{2} \) 2. \( r = -\frac{3}{2} \) ### Step 5: Find corresponding values of \( a \) Now, we can find the corresponding values of \( a \) using the product of the roots: 1. For \( r = \frac{1}{2} \): \[ r \cdot r^2 = \frac{1}{2} \cdot \left(\frac{1}{2}\right)^2 = \frac{1}{2} \cdot \frac{1}{4} = \frac{1}{8} \] Setting this equal to the product of the roots: \[ \frac{1}{8} = \frac{-(a + 3)}{8} \] This simplifies to: \[ 1 = -(a + 3) \implies a + 3 = -1 \implies a = -4 \] 2. For \( r = -\frac{3}{2} \): \[ r \cdot r^2 = -\frac{3}{2} \cdot \left(-\frac{3}{2}\right)^2 = -\frac{3}{2} \cdot \frac{9}{4} = -\frac{27}{8} \] Setting this equal to the product of the roots: \[ -\frac{27}{8} = \frac{-(a + 3)}{8} \] This simplifies to: \[ -27 = -(a + 3) \implies a + 3 = 27 \implies a = 24 \] ### Final Answer The values of \( a \) are \( -4 \) and \( 24 \).
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