How to solve this ???

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1 Answer
Jun 3, 2017

We have a=1a=1 and b=2b=2. For details please see below.

Explanation:

We have 3x^2+6x+53x2+6x+5

= 3(x^2+2x)+53(x2+2x)+5

= 3(x^2+2xx x xx1+1^2)-3xx1^2+53(x2+2×x×1+12)3×12+5

= 3(x+1)^2-3+53(x+1)23+5

= 3(x+1)^2+23(x+1)2+2

Hence a=1a=1 and b=2b=2

As (x+1)^2(x+1)2 is a perfect square, and minimum value of 3x^2+6x+53x2+6x+5 is 22 and hence it is always non-zero and positive and hence 2/(3x^2+6x+5) >=023x2+6x+50

3(x+1)^2>=03(x+1)20 or 3(x+1)^2+2>=23(x+1)2+22

i.e. 3x^2+6x+5 >=23x2+6x+52 and dividing by 3x^2+6x+53x2+6x+5, we get

0 <=2/(3x^2+6x+5) <= 1023x2+6x+51
graph{2/(3x^2+6x+5) [-10, 10, -5, 5]}