If the roots of an equation ax^2 + bx + c = 0 have to become twice their value what should be the change in a and b.

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justaguide | College Teacher | (Level 2) Distinguished Educator

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The roots of the equation ax^2 + bx + c = 0 have to be changed from x1, x2 to 2*x1 and 2*x2 respectively. The change in a and b required for this has to be estimated.

ax^2 + bx + c = 0

=> (x - x1)(x - x2) = 0

=> x^2 - (x1 + x2)*x + x1*x2 = 0 ...(1)

As this has to be in the form ax^2 + bx + c = 0

When the roots become 2*x1 and 2*x2

(x - 2*x1)(x - 2*x2) = 0

=> x^2 - (2*x1 + 2*x2) + 4*x1*x2 = 0

=> x^2 - 2*(x1 + x2) - 4*x1*x2 = 0 ...(2)

Comparing (1) and (2) it is seen that b becomes twice and c becomes 4 times.

The change in ax^2 + bx + c = 0 for the roots to become double are b becomes twice and c becomes 4 times their original value.

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