Finding the Diagonals of a Rhombus, the Dummies Version

Shape of a rhombus

If you've ever watched a political debate, you've probably realized that the best way to avoid answering a potentially embarrassing question is to answer a different question. Political types call this "pivoting to a different topic." Some content-farm freelancers are quite comfortable with the technique, merrily answering one question while pretending to answer another. Take, for example, eHow.com's Jack Ori (real name Stephanie Silberstein): Jack deliberately misread one of his questions and ended up giving only a partial answer to "How to Calculate the Diagonals of Rhombuses."¹

If you read through Ori's instructions, you'll find that just about all our Jack did was reword the instructions anyone can find in many places on the internet. Oh, he started out by defining a rhombus as

"...a parallelogram shape that has four congruent sides..." ...which is essentially correct – partial, but correct. He also mentioned the diagonals of said shape, although he neglected to mention that they're of different lengths (unless, of course, the rhombus is a rectangle). Where Jack got himself into trouble with the DotD selection team is the two sets of instructions he provided. According to Jack, there are two possible scenarios for "Geometry students... asked to calculate how long a diagonal of a particular rhombus": Find the Length Given a Side and the Other Diagonal Find the Length Given the Area and the Other Diagonal

Jack's instructions for the first scenario are correct – so wordy as to be confusing, but correct. His answer for the second case are even more verbose, but are also essentially correct (watching a liberal arts type try to put math into words is... confusing). Where Jack screwed the pooch (this time, anyway) is not in the mathematics he cribbed, which are pretty simple; it's in the grammar of the title. You see, the question asks about diagonals, plural: in both his examples, Ori assumes you already know the length of one diagonal (in math-speak, it's "given").

How do you find the length of that diagonal in the first place? Well, you can't – at least not with simple geometry: you need to use trigonometry (the law of cosines) to find the third side of a triangle in a side-angle-side probem. Jack never mentioned that fact, preferring to concentrate on the simple stuff he sort of understood – and eHow's content editor (probably a J-school grad him- or her-self [most likely herself]) let him get away with it. Classic Dumbass of the Day material, don't you think?

¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was    ehow.com/how_6062606_calculate-diagonals-rhombuses.html

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