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19 votes
19 votes
If x²+y²=20 and x-y=6 how is x.y?


User NeXau
by
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2 Answers

15 votes
15 votes


(x-y)^2=x^2-2xy+y^2

Therefore


6^2=20-2xy\\36=20-2xy\\2xy=-16\\xy=-8

User Jeroen Van Dijk
by
3.2k points
12 votes
12 votes

Answer:

xy = - 8

Explanation:

note that

(x - y)² = x² + y² - 2xy , that is

6² = 20 - 2xy

36 = 20 - 2xy ( subtract 20 from both sides )

16 = - 2xy ( divide both sides by - 2 )

- 8 = xy

User Mareq
by
2.8k points