Complex Numbers And Quadratic Equations question 16
Question: If $ x $ be real, then the maximum value of $ 5+4x-4x^{2} $ will be equal to [MNR 1979]
Options:
A) 5
B) 6
C) 1
D) 2
Show Answer
Answer:
Correct Answer: B
Solution:
Let $ f(x)=5+4x-4x^{2}=y\Rightarrow 4x^{2}-4x-5+y=0 $ Since x is real, so $ B^{2}-4AC\ge 0 $
Þ $ 16-4.4(-5+y)\ge 0 $
Þ $ 16-16(-5+y)\ge 0\Rightarrow -5+y\le 1\Rightarrow y\le 6 $ Hence maximum value of y is 6.
BETA
