f(x), g(x), 2 quadratic polynomials: \(\displaystyle{\left|{f{{\left({x}\right)}}}\right|}≥{\left|{g{{\left({x}\right)}}}\right|}∀{x}∈{R}\). Find the

Oxinailelpels3t14

Oxinailelpels3t14

Answered question

2022-04-05

f(x), g(x), 2 quadratic polynomials:
|f(x)||g(x)|xR. Find the number of distinct roots of equation h(x)h(x)+(h(x))2=0 if h(x)=f(x)g(x)

Answer & Explanation

aznluck4u72x4

aznluck4u72x4

Beginner2022-04-06Added 16 answers

Let f(x)=a(xp)(xq), where a0,p,qR. Then |g(p)||f(p)|=0g(p)=0, so g(x)=b(xp)(xq) for some real b0. Thus we have h(x)=c(xp)2(xq)2 for some real c0.
The condition hh +(h)2=0 is the same as dd dx hh=0.
However, note h(x) has two double roots, hence shares those roots with h'(x). The third root of the cubic h'(x) must also then be real, between those two roots p,q. Thus in all, hh' is a seventh degree polynomial with roots of multiplicity 3 at p,q, and one root at some r between p,q.
This implies the derivative of hh' must have all six roots real, two with multiplicity two at p,q, and one each between p,r and r,q.
Putting it all together, if p,q are distinct, hh +(h)2=0 has four distinct roots, two of multiplicity two at p,q and two distinct ones between p and q. If p=q, then hh +(h)2 has only one root, which however has multiplicity 6.

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