Haryana Police Constable Model Paper 1

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Question : 41 of 100

Marks: +1, -0

If

3\x^{2} + \kx + 12 = 0

have two equal roots then value of k is:

+12
±10
±12
-12

Solution:

Given,
The equation is

= 3\x^{2} + \kx + 12 = 0

Concept:
If

\b^{2} -4\ac = 0

, we get two equal real roots.
Calculation:

⇒3 \x ^{2}+ \kx +12=0

Comparing in

\a\x ^{2}+ \b\x + c =0

\⇒\a =3, \b = \k

\and \c =12

If roots are equal, then

⇒ \b^{2}-4 \a \c=0

⇒\k ^{2}-4 \×3 \×12=0

\⇒\k ^{2}=12 \×12

\⇒ \k =\√{(12 \×12)}

\∴\k =±12

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