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Find the other root

Q.)One root of X2+kX-8=0 is square of the other. Then, the value of k is:
1)2
2)8
3)-8
4)-2

Solution: let the root be a and a2.
Hence , Sum of the roots = -b/a = -k and Product of the roots = c/a = -8

a + a2 = -k
and a * a2 = -8 => a3 = -8
=> a= -2

Hence , a + a2 = -2+(-2)2 = -2 + 4 =2 = -k
=> k =-2 Option(4) Ans.