Math Problem Statement

find the 2 consecutive positive integers sum of whose square is 630

Solution

Let the two consecutive positive integers be xx and x+1x+1. Their squares add up to 630:

x2+(x+1)2=630x^2 + (x+1)^2 = 630

Step 1: Expand the equation

x2+(x2+2x+1)=630x^2 + (x^2 + 2x + 1) = 630

2x2+2x+1=6302x^2 + 2x + 1 = 630

Step 2: Simplify the equation

2x2+2x629=02x^2 + 2x - 629 = 0

Step 3: Divide by 2 to simplify further

x2+x314.5=0x^2 + x - 314.5 = 0

Step 4: Solve using the quadratic formula

The quadratic formula is: x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Here, a=1a = 1, b=1b = 1, and c=314.5c = -314.5. Substituting these values:

x=1±124(1)(314.5)2(1)x = \frac{-1 \pm \sqrt{1^2 - 4(1)(-314.5)}}{2(1)}

x=1±1+12582x = \frac{-1 \pm \sqrt{1 + 1258}}{2}

x=1±12592x = \frac{-1 \pm \sqrt{1259}}{2}

Step 5: Approximate 1259\sqrt{1259}

125935.48\sqrt{1259} \approx 35.48

x=1±35.482x = \frac{-1 \pm 35.48}{2}

Step 6: Calculate the two solutions

x=1+35.482=34.48217.24x = \frac{-1 + 35.48}{2} = \frac{34.48}{2} \approx 17.24

x=135.482=36.48218.24(not positive)x = \frac{-1 - 35.48}{2} = \frac{-36.48}{2} \approx -18.24 \, \text{(not positive)}

Since xx must be an integer, the closest value is x=17x = 17.

Step 7: Verify the solution

The integers are 1717 and 1818. Their squares are:

172+182=289+324=61317^2 + 18^2 = 289 + 324 = 613

Therefore, the two consecutive positive integers are 17 and 18.


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Related Questions

  1. How do you derive the quadratic formula?
  2. What are other methods to solve quadratic equations?
  3. How can we check if a number is a perfect square?
  4. How to solve a system of equations involving consecutive integers?
  5. How can we extend this to sums of cubes?

Tip: Always verify your solution by substituting it back

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Consecutive Integers

Formulas

Quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a
Sum of squares: x^2 + (x+1)^2

Theorems

Quadratic formula
Basic properties of consecutive integers

Suitable Grade Level

Grades 9-11