SOLUTION: find three consecutive integers such that the sum of the squares of the second and the third exceeds the square of the first by 21.

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Question 162007: find three consecutive integers such that the sum of the squares of the second and the third exceeds the square of the first by 21.
Found 4 solutions by SAT Math Tutor, Earlsdon, eperette, josmiceli:
Answer by SAT Math Tutor(36) About Me  (Show Source):
You can put this solution on YOUR website!
Ok, the first thing to do is set up your variables. We will choose 3 consecutive integers using just 1 variable n:
n
n + 1
n + 2
Then, set up the equation:
%28n%2B1%29%5E2%2B%28n%2B2%29%5E2+=+n%5E2+%2B+21
And solve:
n%5E2%2B2n%2B1+%2B+n%5E2%2B4n%2B4+=+n%5E2+%2B+21
2n%5E2%2B6n%2B5+=+n%5E2+%2B+21
n%5E2%2B6n-16+=+0
Then, use the quadratic equation:
%28-6+%2B-+sqrt%286%5E2-4%2A1%2A-16%29%29%2F2
%28-6+%2B-+sqrt%28100%29%29%2F2
%28-6+%2B-+10%29%2F2
This gives you an answer of n = 2, -8
So there are 2 solutions:
2, 3, 4
AND
-8, -7, -6

Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Let the three consecutive integers be: x, (x+1), and (x+2)
%28x%2B1%29%5E2+%2B+%28x%2B2%29%5E2+=+x%5E2%2B21 "...the sum of the squares of the second and third exceed the square of the first by 21." Simplify this and solve for x.
%28x%5E2%2B2x%2B1%29%2B%28x%5E2%2B4x%2B4%29+=+x%5E2%2B21 Combine like-terms.
2x%5E2%2B6x%2B5+=+x%5E2%2B21 Subtract x%5E2 from both sides.
x%5E2%2B6x%2B5+=+21 Subtract 21 from both sides.
x%5E2%2B6x-16+=+0 Solve this quadratic equation by factoring.
%28x-2%29%28x%2B8%29+=+0 Apply the zero product rule.
x-2+=+0 or x%2B8+=+0 so...
x+=+2 or x+=+-8
There are two answers to this problem:
x = 2
(x+1) = 3
(x+2) = 4 and...
x = -8
x+1 = -7
x+2 = -6

Answer by eperette(173) About Me  (Show Source):
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Call the cosecutive integers n,n%2B1,n%2B2
Given:
%28n%2B1%29%5E2+%2B+%28n%2B2%29%5E2+=+n%5E2+%2B+21
n%5E2%2B+2n+%2B+1+%2B+n%5E2+%2B+4n+%2B+4+=+n%5E2+%2B+21
2n%5E2+%2B+6n+%2B+5+=+n%5E2+%2B+21
n%5E2+%2B+6n+-+16+=+0
%28n+%2B+8%29%28n+-+2%29+=+0
Either
n+%2B+8+=+0
n+=+-8
or
n+-+2+=+0
n+=+2
Use the positive result
n%2B1+=+3
n%2B2+=+4
The numbers are 2,3,and 4
check answer:
%28n%2B1%29%5E2+%2B+%28n%2B2%29%5E2+=+n%5E2+%2B+21
3%5E2+%2B+4%5E2+=+2%5E2+%2B+21
9+%2B+16+=+4+%2B+21
25+=+25
OK