SOLUTION: Please help me with this one. The lengths of the diagnols of a rhombus are inthe ratio 2:1. If the perimeter of the rhombus is 20, find the sum of the lengths of the diagnols.

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Question 123308This question is from textbook Geometry for Enjoyment and Challenge New Edition
: Please help me with this one.
The lengths of the diagnols of a rhombus are inthe ratio 2:1.
If the perimeter of the rhombus is 20, find the sum of the lengths of the diagnols.
This question is from textbook Geometry for Enjoyment and Challenge New Edition

Answer by solver91311(24713)   (Show Source): You can put this solution on YOUR website!


Discussion



The diagonals of a rhombus are perpendicular bisectors, so half of one diagonal
half of the other diagonal, and one of the sides of the rhombus form a right
triangle with the rhombus side being the hypotenuse.

Since we know the perimeter and we know that all four sides of the rhombus are
equal, we can calculate the length of the triangle hypotenuse by dividing the
rhombus perimeter by 4.

Since the diagonals mutually bisect each other and the length of the diagonals
are in the ratio 2:1, the measures of the half-diagonals that form the legs of
the triangle must also be in the ratio 2:1.

From here, we can apply the Pythagorean theorem to determine the lengths of the
half-diagonals.





Solution



If we let x be a representation of the measure of the short leg of the triangle
then the measure of the long leg must be represented by 2x.

The perimeter is given as 20, so the length of one side of the rhombus is:


Using Pythagoras,







So the measure of the short leg of the triangle is and the
measure of the short diagonal is . The measure of the long
leg of the triangle is twice the short leg, or so the measure
of the long diagonal is .
is then the sum of the lengths of the diagonals.


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