Quardratic problem

Algebra Level 1

If the sum of the squares of two consecutive positive integers is 313. Then, find the sum of the integers.


The answer is 25.

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3 solutions

Victor Loh
Jul 23, 2015

Let the smaller positive integer be x x . Then the larger positive integer is x + 1 x+1 . We have

x 2 + ( x + 1 ) 2 = 313 \nonumber x 2 + x 2 + 2 x + 1 = 313 \nonumber 2 x 2 + 2 x 312 = 0 \nonumber x 2 + x 156 = 0 \nonumber ( x + 13 ) ( x 12 ) = 0 \nonumber \begin{aligned} x^2 + (x+1)^2 &= 313 \nonumber \\ x^2 + x^2 + 2x + 1 &= 313 \nonumber \\ 2x^2 + 2x - 312 &= 0 \nonumber \\ x^2 + x - 156 &= 0 \nonumber \\ (x+13)(x-12) &=0 \nonumber \end{aligned}

Since x x is positive, x = 12 x=12 . Thus, the sum of the two integers is 12 + 13 = 25 12+13=\boxed{25} .

Bryan Yeo
Jul 23, 2015

Let the first positive integer be x x .

\implies The second positive integer is x + 1 x+1 .

x 2 + ( x + 1 ) 2 = 313 x^2 + (x+1)^2 = 313 2 x 2 + 2 x + 1 = 313 2x^2 +2x + 1 = 313 x 2 + x 156 = 0 x^2+x-156 = 0 ( x 12 ) ( x + 13 ) = 0 (x-12)(x+13)=0 x = 12 or 13 (rej.) x=12 \quad \text{or} \quad -13 \quad \text{(rej.)}

Therefore, sum = 12 + 12 + 1 = 25 = 12+12+1 = \boxed{25} .

Nishant Kumar
Jan 20, 2015

x^2 + y^2 = 313 , y=x+1 , x^2 +x^2 +1 +2x = 313, , 2x^2 +2x-312 = 0, , x^2 +x -156= 0 , x = 12 , y = 13 , 12+13 = 25 Here is your answer

How y=x+1 taken ?

Vaibhav Joshi - 6 years, 4 months ago

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Because they are two consecutive numbers

John Israel - 6 years, 4 months ago

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