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Question

The least value of k which makes the roots of the equation x2+5x+k=0 imaginary is

A
6
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B
7
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C
4
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D
5
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Solution

The correct option is B 7
We have,

x2+5x+k=0

On comparing with general form of Quadratic Equation ax2+bx+c=0

We get a=1, b=5, c=k

As roots are imaginary, so D<0

b24ac<0

(5)24(1)(k)<0

254k<0

4k>25

k>2546.25

Hence, the least value of k from the options is 7.

Option (D) is correct.

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