Evaluating algebraic expression

Algebra Level 3

Evaluate the value of the expression at given value. Be careful when you have (a+b)^2.

Note: Round your answer to the thousandth place.


The answer is 13.472.

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3 solutions

Yang Cheng
Feb 2, 2015

1. E x p a n d a n d r e a r r a n g e t h e e x p r e s s i o n ( 1 + x ) 2 + ( 1 1 x ) 2 = ( 1 + 2 x + x 2 ) + ( 1 2 x + 1 x 2 ) = x 2 + 1 x 2 + 2 ( x 1 x ) + 2 = ( x 1 x ) 2 + 2 ( x 1 x ) + 4 1. \ Expand \ and \ rearrange \ the \ expression \\ (1+x)^2+ \left ( 1- \dfrac{1}{x} \right )^2 \\ =(1+2x+x^2)+ \left (1- \dfrac{2}{x}+ \dfrac{1}{x^2} \right ) \\ =x^2+ \dfrac{1}{x^2} + 2 \left ( x- \dfrac{1}{x} \right ) +2 \\ = \left ( x- \dfrac{1}{x} \right )^2 + 2 \left ( x- \dfrac{1}{x} \right ) +4

2. E v a l u a t e t h e v a l u e o f x 1 x x 1 x = 3 + 5 2 2 3 + 5 = 5 3. P l u g i n x 1 x = 5 t o t h e e x p r e s s i o n a b o v e a n d w e l l g e t 9 + 2 5 = 13.472 ( r o u n d e d t o t h e n e a r e s t t h o u s a n d t h ) 2. \ Evaluate \ the \ value \ of \ x- \dfrac{1}{x} \\ \begin{aligned} x- \dfrac{1}{x} & = \dfrac{3+ \sqrt{5}}{2}- \dfrac{2}{3+\sqrt{5}} \\ & = \sqrt{5} \\ \end{aligned} \\ 3. \ Plug \ in \ x- \dfrac{1}{x}= \sqrt{5} \ to \ the \ expression \ above \ and \ we'll \ get \\ 9+2\sqrt{5}= \boxed{13.472} \quad (rounded \ to\ the \ nearest \ thousandth)

Amazing! I haven't thought of this.

Joeie Christian Santana - 6 years, 4 months ago
Stanley Guo
Jan 29, 2015

Plug in and simplify.

Lu Chee Ket
Jan 29, 2015

Apply calculator for 13.472 as answer.

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