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5x^(2) - 15x-4=0

completing the square

User Lloyd
by
8.5k points

1 Answer

3 votes

Answer:

x = 3/2 ± √(61/20)

Explanation:

5x² - 15x - 4 = 0

Add 4 to both sides.

5x² - 15x = 4

The coefficient of 5x² is 5, divide both sides by 5.

x² - 3x = 4/5

The coefficient of -3x is -3. Let b=-3.

Then we need to add (b/2)^2=9/4 to both sides to complete the square.

Add 9/4 to both sides.

x² - 3x + 9/4 = 61/20

Factor left side.

(x-3/2)² = 61/20

Take square root of both sides.

x-3/2 = ± √(61/20)

Add 3/2 to both sides.

x = 3/2 ± √(61/20)

User Scott Kilbourn
by
8.2k points

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