Degree of polynomial

Algebra Level 4

[ x + ( x 3 1 ) 1 2 ] 5 + [ x ( x 3 1 ) 1 2 ] 5 \large \left[{x + (x^3 -1)^{\frac12}}\right]^5 + \left[{x - (x^3 -1)^{\frac12}}\right]^5

What is the degree of the polynomial given above?


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7 9 4 6 5 8

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2 solutions

Chew-Seong Cheong
Jan 28, 2016

Let y = ( x 3 1 ) 1 2 y = (x^3-1)^{\frac{1}{2}} . Then:

\left(x + (x^3-1)^{\frac{1}{2}} \right)^5 + \left(x - (x^3-1)^{\frac{1}{2}} \right)^5 \\ = \left(x + y \right)^5 + \left(x - y \right)^5 \\ = x^5 \color{#D61F06}{+ 5x^4y} + 10 x^3y^2 \color{#D61F06}{+ 10 x^2y^3} + 5xy^4 \color{#D61F06}{+ y^5} + x^5 \color{#D61F06}{- 5x^4y} + 10 x^3y^2 \color{#D61F06}{- 10 x^2y^3} + 5xy^4 \color{#D61F06}{- y^5} \\ = 2x^5 + 20 x^3y^2 + 10xy^4 \\ = 2x^5 + 20 x^3(x^3-1) + 10\color{#3D99F6}{x(x^3-1)^2} \\ = 2x^5 + 20 x^3(x^3-1) + 10(\color{#3D99F6}{x^\boxed{7}-2x^4+x})

Therefore, the degree of the polynomial is 7 \boxed{7} .

汶良 林
Jan 31, 2016

So the degree of the polynomial is 7 . \boxed{7}.

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