Large Surd

Algebra Level 3

2000 × 2008 × 2009 × 2017 + 1296 \large \sqrt{2000 \times 2008 \times 2009 \times 2017 + 1296}

What is the value of the above expression?


The answer is 4034036.

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1 solution

Let x = 2000 x=2000 . We have 2000 × 2008 × 2009 × 2017 + 1296 = x ( x + 17 ) ( x + 8 ) ( x + 9 ) + 1296 = ( x 2 + 17 x ) ( x 2 + 17 x + 72 ) + 1296 \sqrt{2000×2008×2009×2017+1296}=\sqrt{x(x+17)(x+8)(x+9)+1296}=\sqrt{(x^2+17x)(x^2+17x+72)+1296}

Let y = x 2 + 17 x + 36 y=x^2+17x+36 . ( x 2 + 17 x ) ( x 2 + 17 x + 72 ) + 1296 = ( y 36 ) ( y + 36 ) + 1296 = y 2 = y \sqrt{(x^2+17x)(x^2+17x+72)+1296}=\sqrt{(y-36)(y+36)+1296}=\sqrt{y^2}=y .

The answer is y = x 2 + 17 x + 36 = 200 0 2 + 17 × 2000 + 36 = 4034036 y=x^2+17x+36=2000^2+17×2000+36=4034036 .

Nice usage of the substitution to simplify the calculations :)

Calvin Lin Staff - 4 years, 6 months ago

REALLY GOOD.......................I also used the same

anshu garg - 4 years, 6 months ago

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