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Here,

It is given in the question that,                                                    

Length of a rectangle = 40 cm                                                              

Diagonal of a rectangle = 41 cm

We know that,

Diagonal of a rectangle divides it into two right-angled triangles

By using Pythagoras theorem, we get

(Diagonal)² = (Length)² + (Breadth)²

(41)² = (40)² + b²

b² = (41)² – (40)²

b²= 1681 – 1600

b² = 81

b =

b = 9 cm

Thus,

Perimeter of rectangle = 2 (l + b)

= 2 (40 + 9)

= 2 (49)

= 98 cm