Why does first cosine theorem work for a triangle that doesn't exist?

Given , where , , , and , what's the length of a?

The triangle doesn't exist, because the hypotenuse cannot be the same length as one of the other sides. But when you put it in the first cosine theorem, it gives an answer



???

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Originally Posted by chengbin

Given , where , , , and , what's the length of a?

The triangle doesn't exist, because the hypotenuse cannot be the same length as one of the other sides. But when you put it in the first cosine theorem, it gives an answer



???

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You should know that, for a right angled triangle, the law of cosines reduces to

This will give you

what is the "first cosine theorem" ?

never heard of it.

Umm, just realized that this doesn't exist (???)

What I learned was