SOLUTION: Can you please solve this for me? I have to solve this using factoring: The sum of the squares of two consecutive negative even integers is 340. Find the integers.

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Question 33038: Can you please solve this for me? I have to solve this using factoring:
The sum of the squares of two consecutive negative even integers is 340. Find the integers.

Found 3 solutions by xcentaur, ikleyn, greenestamps:
Answer by xcentaur(357) About Me  (Show Source):
You can put this solution on YOUR website!
sum of the squares of two consecutive negative even integers is 340


let the first number be x
it must be negative and even,so it becomes '-2x'
Then the second number becomes '-2x+2'


So we get,
(-2x)^2+(-2x+2)^2=340
4x^2+(4x^2+4-8x)=340
8x^2-8x+4-340=0
8x^2-8x-316=0


Solve for x. then '-2x' and '-2x+2' give you the required numbers

Answer by ikleyn(53742) About Me  (Show Source):
You can put this solution on YOUR website!
.
.
Can you please solve this for me? I have to solve this using factoring:
The sum of the squares of two consecutive negative even integers is 340. Find the integers.
~~~~~~~~~~~~~~~~~~~~~~~~~


        I will solve it in as simple way as I can.


We are looking for two consecutive even integer numbers n and (n+2).


I will start from the central integer number 'm' between n and (n+2), so that

    n = m-1,  n+2 = m+1.


Then my equation is

    (m-1)^2 + (m+1)^2 = 340,

    (m^2 - 2m + 1) + (m^2 + 2m + 1) = 340,

     2m^2 + 2 = 340,

     2m^2 = 340 - 2 = 338,

      m^2 = 338/2 = 169,

      m = +/- sqrt%28169%29 = +/- 13.


We are looking for two consecutive negative numbers, so these numbers are -14 and - 12.    ANSWER


CHECK.  (-14)^2 + (-12)^2 = 196 + 144 = 340.    ! Precisely correct !

Notice that the other tutor reduced the problem to solution of a quadratic equation, but left the solution to you.

I solved the problem completely in a simplest way, practically mentally
to the end, without solving a quadratic equation.



Answer by greenestamps(13326) About Me  (Show Source):
You can put this solution on YOUR website!


(1) Following the directions to solve the problem using factoring....

Let the smaller integer be x; then the larger integer is x+2. The sum of the squares is 340, and the integers are negative:

x%5E2%2B%28x%2B2%29%5E2=340
x%5E2%2Bx%5E2%2B4x%2B4=340
2x%5E2%2B4x-336=0
x%5E2%2B2x-168=0
%28x%2B14%29%28x-12%29=0
x=-14 or x=12

The integers are negative, so the smaller integer is x = -14 and the large integer is x+2 = -12.

ANSWERS: -14 and -12

(2) Being smart about how you use algebra....

Use the powerful "trick" shown by tutor @ikleyn -- instead of using x and x+2 for the two integers, use x-1 and x+1. Then

%28x-1%29%5E2%2B%28x%2B1%29%5E2=340
x%5E2-2x%2B1%2Bx%5E2%2B2x%2B1=340
2x%5E2=338
x%5E2=169
x=13 or x=-13

The answers have to be negative, so x is -13 and the two integers are x-1 = -14 and x+1 = -12.

As you can see, using this trick leads to an equation that is easily solved and does not require the use of factoring. That's the reason for using the trick (in this and similar problems).

(3) Solving the problem as quickly as possible -- as if you are taking a timed competitive exam.

Solve informally using logical reasoning and mental arithmetic.

Half of 340 is 170.

What are the two squares of even integers that are closest to and on opposite sides of 170? They are 12^2 = 144 and 14^2 = 196.

The answers have to be negative, so they are -14 and -12.