If the side of a rhombus is $25$ cm and one diagonal is $30$ cm, the length of the other diagonal is:

If the side of a rhombus is $25$ cm and one diagonal is $30$ cm, the length of the other diagonal is:
  1. $20$ cm
  2. $40$ cm
  3. $35$ cm
  4. $45$ cm

Solution

Half the known diagonal $= 15$. Half the other diagonal $= \sqrt{25^{2}-15^{2}} = \sqrt{400} = 20$. So other diagonal $= 40$ cm.

Asked in: IMO

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