The integral value of k for which the equation (k−2)x2+8x+k+4=0 has both the roots real, distinct and negative is
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a
0
b
2
c
3
d
−4
answer is C.
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Detailed Solution
Given equation is (k−2)x2+8x+k+4=0 …( 1 ) Given that roots are real and distinct, therefore, 82−4 (k−2)(k+4)>0 (∵b2−4ac>0) ⇒ 16− {k2+2k−8}>0 ⇒ k2+2k−24<0 ⇒ (k+6)(k−4)<0 ⇒ −60 (∵ S =sum of the roots, P = product of the roots )From ( 1 ): S=−8k−2 , P=k+4k−2 ⇒ −8k−2<0 and k+4k−2>0 ⇒ 1k−2>0 and k+4k−2>0 ⇒ k−2>0 and k+4k−2>0 ⇒ k−2>0 and k+4>0 ⇒ k>2 and k>−4 …. ( 3 )From ( 2 ) and ( 3 ) :2