If x – y = 2 and x2 + y2 = 20, then value of (x + y)2

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(x – y)² = x² + y² – 2xy
⇒ 2² = 20 – 2xy
⇒ 2xy = 20 – 4 = 16
∴ (x + y)² = x² + y² + 2xy
= 20 + 16 = 36