SOLUTION: Solve: 3(x^2-3x) = 81

Algebra ->  Customizable Word Problem Solvers  -> Numbers -> SOLUTION: Solve: 3(x^2-3x) = 81      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 205851: Solve:
3(x^2-3x) = 81
Answer by algebrapro18(249) About Me  (Show Source):
You can put this solution on YOUR website!
3(x^2-3x) = 81

now we divide both sides by 3 and get

x^2-3x = 27

now subtract 27 from both sides

x^2-3x-27 = 0

now we factor. So what are the factors of -27:

1, 27
3, 9

hmm so it won't factor...so now we use the quadratic method.

x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ where a = 1, b = -3, and c -27

so plugging in and simplifying we end up with

x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
x+=+%283+%2B-+sqrt%28+9-4%2A1%2A-27+%29%29%2F%282%2A1%29+
x+=+%283+%2B-+sqrt%28+9%2B108+%29%29%2F%282%29+
x+=+%283+%2B-+sqrt%28+117+%29%29%2F%282%29+

Now we know that 117 = 9*13 so the %28sqrt%28117%29%29 = %28sqrt%289%2A13%29%29 and we
know the square root of 9 is 3 so we can pull that out and we get:

x+=+%283+%2B-+3+%2A+sqrt%28+13+%29%29%2F%282%29+

which is as simplified as this gets. If your professor wants this in decimal form it comes out to x = 8.4083 and x = -2.4083