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If using the method of completing the square to solve the quadratic equation x2 – 3x + 20 = 0, which number would have to be added to "complete the square"?​

User PushStack
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1 Answer

7 votes

Answer:

⁹/₄

Explanation:

The square is: a²-2ab+b²

We have


x^2-3x

it's:
x^2-2\cdot x\cdot\frac32

so we need:
\left(\frac32\right)^2=\frac94


x^2-2\cdot x\cdot\frac32+\frac94-\frac94+20=0\\\\(x-\frac32)^2-2.25+20=0\\\\(x-\frac32)^2=-17.75

witch, of course, means no solution

User Robpal
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