# If A = [31-12], prove that A2 – 5A + 7I = 0, where I is unit matrix of order 2 - Mathematics and Statistics

Sum

If A = [(3, 1),(-1, 2)], prove that A2 – 5A + 7I = 0, where I is unit matrix of order 2

#### Solution

A2 = A · A = [(3, 1),(-1, 2)] [(3, 1),(-1, 2)]

= [(9 - 1, 3 + 2),(-3 - 2, -1 + 4)]

= [(8, 5),(-5, 3)]

∴ A2 – 5A + 7I = [(8, 5),(-5, 3)] -5[(3, 1),(-1, 2)] + 7[(1, 0),(0, 1)]

= [(8, 5),(-5, 3)] - [(15, 5),(-5, 10)] + [(7, 0),(0, 7)]

= [(8 - 15 + 7, 5 - 5 + 0),(-5 + 5 + 0, 3 - 10 + 7)]

= [(0, 0),(0, 0)]

= 0.

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#### APPEARS IN

Balbharati Mathematics and Statistics 1 (Arts and Science) 11th Standard Maharashtra State Board
Chapter 4 Determinants and Matrices
Exercise 4.6 | Q 15 | Page 95