SOLUTION: I need help with (n+3)(n-7)=4. I tried it and got an incorrect answer. i attempted like so: (n+3)(n-7)=4 n^2-4n-21=4 n^2-4n=25 n^2+n=-5 sqrt(n^2+n)=sqrt(-5) and thats when i

Algebra ->  Distributive-associative-commutative-properties -> SOLUTION: I need help with (n+3)(n-7)=4. I tried it and got an incorrect answer. i attempted like so: (n+3)(n-7)=4 n^2-4n-21=4 n^2-4n=25 n^2+n=-5 sqrt(n^2+n)=sqrt(-5) and thats when i      Log On


   

Question 791496: I need help with (n+3)(n-7)=4.
I tried it and got an incorrect answer. i attempted like so:
(n+3)(n-7)=4
n^2-4n-21=4
n^2-4n=25
n^2+n=-5
sqrt(n^2+n)=sqrt(-5)
and thats when i knew i was wrong
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
(n+3)(n-7)=4

n^2 - 7n + 3n - 21 = 4

n^2 - 7n + 3n - 21 - 4 = 0

n^2 - 4n - 25 = 0

Now I'm going to use the quadratic formula to solve for n

n+=+%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F%282a%29

n+=+%28-%28-4%29%2B-sqrt%28%28-4%29%5E2-4%281%29%28-25%29%29%29%2F%282%281%29%29 Plug in a+=+1, b+=+-4, c+=+-25

n+=+%284%2B-sqrt%2816-%28-100%29%29%29%2F%282%29

n+=+%284%2B-sqrt%2816%2B100%29%29%2F%282%29

n+=+%284%2B-sqrt%28116%29%29%2F2

n+=+%284%2Bsqrt%28116%29%29%2F2 or n+=+%284-sqrt%28116%29%29%2F2

n+=+%284%2B2%2Asqrt%2829%29%29%2F2 or n+=+%284-2%2Asqrt%2829%29%29%2F2

n+=+2%2Bsqrt%2829%29 or n+=+2-sqrt%2829%29

n+=+7.385165 or n+=+-3.385165

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Exact Solutions: n+=+2%2Bsqrt%2829%29 or n+=+2-sqrt%2829%29

Approximate Solutions: n+=+7.385165 or n+=+-3.385165