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The sum of all integral values of 'a' fo...

The sum of all integral values of 'a' for which the equation `2x ^(2) -(1+2a) x+1 +a=0` has a integral root.

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To solve the problem, we need to determine the sum of all integral values of 'a' for which the quadratic equation \[ 2x^2 - (1 + 2a)x + (1 + a) = 0 \] has integral roots. ### Step-by-Step Solution: 1. **Identify Coefficients**: The quadratic equation can be expressed in the standard form \( ax^2 + bx + c = 0 \) where: - \( a = 2 \) - \( b = -(1 + 2a) \) - \( c = 1 + a \) 2. **Calculate the Discriminant**: The discriminant \( D \) of a quadratic equation \( ax^2 + bx + c = 0 \) is given by: \[ D = b^2 - 4ac \] Substituting the values of \( a \), \( b \), and \( c \): \[ D = (-(1 + 2a))^2 - 4 \cdot 2 \cdot (1 + a) \] \[ D = (1 + 2a)^2 - 8(1 + a) \] 3. **Expand the Discriminant**: Expanding \( D \): \[ D = (1 + 4a + 4a^2) - (8 + 8a) \] \[ D = 4a^2 - 4a - 7 \] 4. **Set Discriminant to be a Perfect Square**: For the roots to be integral, the discriminant \( D \) must be a perfect square. Let \( k^2 = 4a^2 - 4a - 7 \) for some integer \( k \): \[ 4a^2 - 4a - (k^2 + 7) = 0 \] 5. **Calculate the Discriminant of the New Quadratic**: The new quadratic in terms of \( a \): \[ D' = (-4)^2 - 4 \cdot 4 \cdot (-(k^2 + 7)) \] \[ D' = 16 + 16(k^2 + 7) = 16k^2 + 128 \] For \( a \) to be integral, \( D' \) must be a perfect square. 6. **Finding Integral Values of 'a'**: We can find integer values of \( a \) by substituting different integer values for \( k \): - For \( k = 0 \): \( 4a^2 - 4a - 7 = 0 \) gives no integer solutions. - For \( k = 1 \): \( 4a^2 - 4a - 8 = 0 \) gives no integer solutions. - For \( k = 2 \): \( 4a^2 - 4a - 11 = 0 \) gives no integer solutions. - For \( k = 3 \): \( 4a^2 - 4a - 16 = 0 \) gives \( a = 4 \) or \( a = -1 \). - For \( k = 4 \): \( 4a^2 - 4a - 23 = 0 \) gives no integer solutions. - For \( k = 5 \): \( 4a^2 - 4a - 32 = 0 \) gives no integer solutions. 7. **Sum of Acceptable Values of 'a'**: The acceptable values of \( a \) are \( 4 \) and \( -1 \). Therefore, the sum of all integral values of \( a \) is: \[ 4 + (-1) = 3 \] ### Final Answer: The sum of all integral values of 'a' for which the equation has integral roots is \( 3 \).
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VIKAS GUPTA (BLACK BOOK) ENGLISH-QUADRATIC EQUATIONS -EXERCISE (SUBJECTIVE TYPE PROBLEMS)
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