SOLUTION: 2x^2+3x-9=0 Complete the Square. I know how to do it all the way up till when it should look like this: x^2+ (3x/2)+(9/16)=(81/4)+(9/16). It's adding the fractions to the right

Question 877947: 2x^2+3x-9=0 Complete the Square.
I know how to do it all the way up till when it should look like this: x^2+ (3x/2)+(9/16)=(81/4)+(9/16). It's adding the fractions to the right that doesn't make sense. I get 90/64, but mymathlab tells me i should have 81/16. **ugh* my mathlab makes everything more complicated by making me square root and square and cube fractions, and not put it in decimal form, so some help would be much obliged.
Answer by richard1234(7193) (Show Source): You can put this solution on YOUR website!
Easier would be to factor 2 out first: 2(x^2 + (3/2)x - 9/2)

Since half of 3/2 is 3/4, we want it to look something like 2(x + 3/4)^2 + constant. 2(x + 3/4)^2 has a constant term of 2*(3/4)^2 = 9/8, and we want 9, so add 63/8.

Completed square form: 2(x + 3/4)^2 + 63/8 (can be checked via Wolfram Alpha)

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