If x2 + y2 = 9 and xy = 8, then x + y is equal to

If x² + y² = 9 and xy = 8, then x + y is equal to

(a) 25

(b) 5

(c) -5

(d) ± 5

Answer : (d) ± 5

Hint:

x² + y² = 9, xy = 8

Or, x² + y² + 2xy = 9 + 2xy

Or, (x² + y)² = 9 + 2 × 8

Or, x + y = √25 = ± 5

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