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Which of the following can be the sides of a right angled triangle ?

  • A.20 cm, 21 cm and 31 cm
  • B.35 cm, 77 cm and 88 cm
  • C.15 cm, 32 cm and 57 cm
  • D.65 cm, 72 cm and 97 cm

Answer: D

The sides 65 cm, 72 cm and 97 cm can form a right angled triangle.

A triangle is right angled exactly when the square of the longest side equals the sum of the squares of the other two (the converse of Pythagoras' theorem).

\[ \begin{aligned} 65^{2} + 72^{2} &= 4225 + 5184 \\ &= 9409 = 97^{2} \end{aligned} \]

The others fail: \(20^{2} + 21^{2} = 841 = 29^{2}\), not \(31^{2}\); \(35^{2} + 77^{2} = 7154\), not \(88^{2} = 7744\); and 15, 32, 57 cannot even form a triangle, since \(15 + 32 \lt 57\).

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