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The discussion centers on constructing a sixth-degree polynomial with specific factors and characteristics. It emphasizes that multiple polynomials can meet the criteria, including repeated linear factors and a quadratic factor without real roots. The essential factors identified are (x - 1), (x + 1), and (x - 2), but additional factors must be included to reach the required degree. Various combinations of these factors, such as $(x- 1)^4(x- 2)(x+ 1)$ or $(x-1)^2(x- 2)^2(x+ 1)^2$, are suggested. Additionally, any non-zero constant can be multiplied with the product of these factors.
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Any product of (x - 1), (x + 1), (x - 2) and a constant, with some repeated linear factors, quadratic factor without any real roots, or irreducible cubic factor that has 1, -1 or 2 as its roots.
 
What kind of "help" do want? For one thing, there is no single answer. There are many polynomials that satisfy these conditions! The only factors must be (x- 1), (x+ 1), and (x- 2) but that is only three and for a sixth degree polynomial you need six so some factors must be repeated. That could be $(x- 1)^4(x- 2)(x+ 1)$ or $(x-1)^2(x- 2)^2(x+ 1)^2$ or any combination of exponents that add to six. Also, the product of factors can be multiplied by any non-zero constant.
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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