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If: 2x+y = 1 then y =1-2x and y^2 = (1-2x)^2 which is 1-4x+4x^2

If: x^2 -xy -y^2 = -11 then x^2 -x(1-2x) -(1-4x+4x^2) = -11

Expanding brackets: x^2 -x +2x^2 -1 +4x -4x^2 = -11

Collecting like terms and adding 11 to both sides: -x^2 +3x +10 = 0

Dividing all terms by -1: x^2 -3x -10 = 0

Completing the square: (x-3/2)^2 -9/4 -10 = 0 => (x-3/2)^2 = 49/4

Square root both sides: x-3/2 = -/+ 7/2

Add 3/2 to both sides: x = 3/2 -/+ 7/2

Therefore: x = 5 or x = -2

Solutions by substitution are: (5, -9) and (-2, 5)

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7y ago
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7y ago

They are (-2, 5) and (5, -9).

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Q: What are the solutions to the simultaneous equations of x squared -xy - y squared equals -11 and 2x plus y equals 1 solved by completing the square?
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