sandy wrote:

If \(x^2 - 2xy = 84\) and \(x - y = -10\), what is the value of |y|?

Another approach is to use

substitutionGiven:

x - y = -10x² - 2xy = 84Solve the top equation for x to get:

x = y - 10Take the bottom equation and replace x with (y - 10) to get:

(y - 10)² - 2(y - 10)y = 84Expand left side to get: y² - 20y + 100 - 2y² + 20y = 84

Simplify: -y² + 100 = 84

Subtract 100 from both sides to get: -y² = -16

Divide both sides by -1 to get: y² = 16

Solve: y = 4 OR y = -4

In both cases, |y| = 4

Answer: 4

Cheers,

Brent

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Brent Hanneson – Creator of greenlighttestprep.com

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