If x∈R, then the maximum and minimum values of x2+14x+9x2+2x+3 are
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a
3,1
b
0, −∞
c
4, −5
d
∞, −∞
answer is C.
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Detailed Solution
Let the given condition x2+14x+9x2+2x+3 =m, then ⇒(1−m)x2+(14−2m)x+ (9−3m)=0But x∈R, therefore, (14−2m)2−4.(1−m)(9−3m) ≥0 (∵ if x is real ⇒b2−4ac≥0 )⇒ 4m2−56m+196−12m2+48m−36≥0 ⇒ −8m2−8m+160 ≥0 ⇒ m2+m−20 ≤ 0 ⇒ (m+5) (m−4) ≤0 ⇒-5⩽m≤4 ∴ maximum value = 4and minimum value = −5