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Given, A =

∴ A² =

By matrix multiplication we can write:

A² =

⇒ A² = …(1)

As we have to find: A² – 5A – 14I

∴ A² – 5A – 14I =

⇒ A² – 5A – 14I =

⇒ A² – 5A – 14I =

⇒ A² – 5A – 14I = = O

We need to find value of A³ using the above equation:

Now we have,

A² – 5A – 14I = O

⇒ A² = 5A + 14I

Multiplying with A both sides

⇒ A².A = 5A.A + 14IA

⇒ A³ = 5A² + 14A

Using equation 1 we get:

⇒ A³ =

⇒ A³ =

⇒ A³ =