Proof:
Part (1): To show 2x2+5x+3>x2+3x+1 for ∀x∈R,
First, subtract the right-hand side from the left-hand side:
(2x2+5x+3)−(x2+3x+1)=2x2+5x+3−x2−3x−1=x2+2x+2=(x+1)2+1.
Since for ∀x∈R, we have (x+1)2≥0, thus (x+1)2+1>0.
Therefore, it follows that 2x2+5x+3>x2+3x+1.
Part (2): To show a>b for a>b>0,
Consider the difference a−b:
a−b=a+b(a−b)(a+b)=a+ba−b.
Given that a>b>0, it implies a−b>0. Also, since a>0 and b>0, a+b>0.
Therefore, we have a+ba−b>0, which implies a>b.
Thus, the proofs for both parts are as follows:
For part (1): 2x2+5x+3>x2+3x+1 is true for all x∈R.
For part (2): a>b for a>b>0.
Final conclusions are:
- For part (1): 2x2+5x+3>x2+3x+1 True
- For part (2): a>b True