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Q.

If α and β be the roots of x2 + 7x + 12 = 0, find the quadratic equation whose roots are (α + β)2 and (α - β)2.

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a

49x2 - 50x + 49 = 0

b

x2 - 50x + 49 = 0

c

50x2 - 50x + 1 = 0

d

x2 - 50x + 50 = 0

answer is C.

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Detailed Solution

Given: α and β be the roots of x2 + 7x + 12 = 0.

Then, sum of roots = - coefficient of x/coefficient of x2

=> α + β = - 71 = -7 ------ (i)

The product of roots = constant termcoefficient of x2

=> αβ = 121 = 12 ------(ii)

Quadratic equation with roots (α + β)2 and (α - β)2 is:

x2 - [(α + β)2 + (α - β)2]x + (α + β)2(α - β)= 0   ---- (iii)

For the values of (α + β)2 and (α - β)2:

=> (α + β)= (-7)2

=>  (α + β)= 49

Now, (α - β)= (α + β)2 - 4αβ

=> (α - β)= (-7)2 - 4(12) .....{from (i) & (ii)}

=> (α - β)= 49 - 48

=> (α - β)= 1

Putting all the values in (iii), we get:

=>  x2 - [49 + 1]x + 49 ⋅ 1 = 0

=> x2 - 50x + 49 = 0

 

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