To the power 2001!

Algebra Level 4

Find the only real root of this equation
2 x 2001 + 3 x 2000 + 2 x 1999 + 3 x 1998 + + 2 x + 3 = 0 2x^{2001}+3x^{2000}+2x^{1999}+3x^{1998}+\cdots+2x+3=0


The answer is -1.5.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Chew-Seong Cheong
Jun 21, 2016

2 x 2001 + 3 x 2000 + 2 x 1999 + 3 x 1998 + + 2 x + 3 = 0 ( 2 x + 3 ) ( x 2000 + x 1998 + x 1996 + x 1994 + + 1 ) = 0 x = 3 2 Note that x 2000 + x 1998 + x 1996 + + 1 > 0 has no real root = 1.5 \begin{aligned} 2x^{2001}+3x^{2000}+2x^{1999}+3x^{1998}+\cdots+2x+3 & = 0 \\ (2x+3) (x^{2000}+x^{1998}+x^{1996}+x^{1994} + \cdots+1) & = 0 \\ \implies x & = - \frac 32 \quad \quad \small \color{#3D99F6}{\text{Note that }x^{2000}+x^{1998}+x^{1996}+ \cdots+1 > 0 \text{ has no real root}} \\ & = \boxed{-1.5} \end{aligned}

Same solution sir .

Achal Jain - 4 years, 12 months ago

good one...+1

Ayush G Rai - 4 years, 11 months ago
Istiak Reza
Jun 27, 2016

We could also use vieta..note that for an n degree polynomial, sum of the zeroes of that polynomial is simply -coefficient of (n-1)th degree term/coefficient of nth degree term..thus this simply comes out to be 3 2 \frac {-3}{2}

yeah and complex conjugates should cancel one other

gaurav gupta - 4 years, 11 months ago

Yup..certainly..i should've mentioned that..tnx @Gaurav

Istiak Reza - 4 years, 11 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...