X+y = - 4, xy = - 21 what is x and what is y

Question

Mathematics

Carlos Dunn

23 October, 20:16

X+y = - 4, xy = - 21 what is x and what is y

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Answers (1)

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Ernest Lee · Answer 1

X = - 4 - y;

Then, (-4 - y) y = - 21;

Finally, we solve the question: y^2 + 4y - 21 = 0;

We have a = 1, b = 4, c = - 21;

We calculate: b^2 - 4ac = 16 + 84 = 100;

We have y1 = ( - 4 + 10) / 2 = 3; y2 = (-4 - 10) / 2 = - 7;

x1 = - 4 - 3 = - 7; x2 = - 4 + 7 = 3;