Question

Adjacent sides of a parallelogram are $11$ cm and $17$ cm. If the length of one of its diagonals is $26$ cm, find the length of the other diagonal of parallelogram (in cm.).

Answer 1

The sum of the squares of the diagonals of a parallelogram is the sum of the squares of its sides. So,

${26}^2+d^2={11}^2+{17}^2+{11}^2+{17}^2\Rightarrow d=12$