Option 2 : 69696

**Given∶**

**Formula Used∶**

^{2}

^{2}

^{2}

**Calculation∶**

By using Duplex,

⇒ 264^{2}

⇒^{ }D(2) = 2^{2} = 4

⇒ D(26) = 2 × (2 × 6) = 24

⇒ D(264) = 2 × (2 × 4) + 6^{2} = 52

⇒ D(64) = 2 × (6 × 4) = 48

⇒ D(4) = 4^{2} = 16

Without considering the plus sign, write the number as shown below 4 + 24 + 52 + 48 + 16

**∴ The square of 264 is 69696.**