Factorize

Algebra Level 2

Factorize 5 x 2 + 20 x + 25 5x^2+20x+25 .

(2x+3)^2+(x+4)^2 (x+2)^2+(x+1)^2 (3x+4)^2+(x+1)^2 (3x+5)^2+(x+1)^2

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2 solutions

Hung Woei Neoh
May 26, 2016

Multiple choice method (the lazy method):

Just calculate how many x 2 x^2 each of the choices has

( x + 2 ) 2 + ( x + 1 ) 2 = ( x 2 + ) + ( x 2 + ) = 2 x 2 + ( 2 x + 3 ) 2 + ( x + 4 ) 2 = ( 4 x 2 + ) + ( x 2 + ) = 5 x 2 + ( 3 x + 4 ) 2 + ( x + 1 ) 2 = ( 9 x 2 + ) + ( x 2 + ) = 10 x 2 + ( 3 x + 5 ) 2 + ( x + 1 ) 2 = ( 9 x 2 + ) + ( x 2 + ) = 10 x 2 + (x+2)^2 + (x+1)^2 = (x^2 + \ldots) + (x^2 + \ldots) = 2x^2 + \ldots\\ (2x+3)^2 + (x+4)^2 = (4x^2 + \ldots) + (x^2 + \ldots) = 5x^2 + \ldots\\ (3x+4)^2+(x+1)^2= (9x^2 + \ldots) + (x^2 + \ldots) = 10x^2 + \ldots\\ (3x+5)^2+(x+1)^2= (9x^2 + \ldots) + (x^2 + \ldots) = 10x^2 + \ldots

Pretty obvious, only ( 2 x + 3 ) 2 + ( x + 4 ) 2 \boxed{(2x+3)^2 + (x+4)^2} satisfies the original expression.

Translation of the solution given by problem setter:

5 x 2 + 20 x + 25 = 4 x 2 + 12 x + 9 + x 2 + 8 x + 16 = ( 2 x ) 2 + 2 ( 2 x ) ( 3 ) + 3 2 + x 2 + 2 ( x ) ( 4 ) + 4 2 = ( 2 x + 3 ) 2 + ( x + 4 ) 2 5x^2+20x+25\\ =4x^2+12x+9+x^2+8x+16\\ =(2x)^2 + 2(2x)(3) + 3^2 + x^2 + 2(x)(4) + 4^2\\ =\boxed{(2x+3)^2 + (x+4)^2}

Tahmid Chowdhury
Apr 24, 2016

5x^2+20x+25 =4x^2+12x+9+x^2+8x+16 =(2x)^2+2 2x 3+(3)^2+x^2+8x+(4)^2 =(2x+3)^2+(x+4)^2

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