Question by Lionel Messi - Discuss with MathYouLike

Lionel Messi

19/03/2017 at 11:43

If (x+y)² = 9 and (x-y)² = 1, x² + y² = ?

Operation of Indices

List of answers

FA KAKALOTS 06/02/2018 at 12:30

(x + y)2 = 9

<=> x2 + 2xy + y2 = 9 (1)

(x - y)2 = 1

<=> x2 - 2xy + y2 = 1 (2)

(1) - (2) => 4xy = 8 => xy = 2

=> x2 + 2xy + y2 = 9

<=> x2 + 4 + y2 = 9

<=> x2 + y2 = 5
Hồ Thu Giang 19/03/2017 at 14:36

(x + y)² = 9

<=> x² + 2xy + y² = 9 (1)

(x - y)² = 1

<=> x² - 2xy + y² = 1 (2)

(1) - (2) => 4xy = 8 => xy = 2

=> x² + 2xy + y² = 9

<=> x² + 4 + y² = 9

<=> x² + y² = 5

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