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# I need clarification on a previous answer to a geometry proof.

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https://web2.0calc.com/questions/help-with-proof

I found this and everything makes sense.

But I don't understand how CPhill got to 2xh  + 2yh   =  2ab . I tried working out and expanding the given equation in the problem and using the triangle similarity he provided in an attempt to get what he got, but I don't understand how. Does anyone understand and can explain this part to me? Thank you!

Jul 6, 2020

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You can use the area formula.

Jul 6, 2020
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I asked for how CPhill got that expression...

Can anybody else help?

gwenspooner85  Jul 6, 2020
edited by gwenspooner85  Jul 6, 2020
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x2 + 2xh + h2 + y2 + 2yh + h2  =  x2 + h2 + 2ab + y2 + h2

Subtract x2, h2, y2, and h2 from both sides and you are left with:  2xh + 2yn  =  2ab

Jul 6, 2020
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Oh I see...I didn't see the OP's working. However, I don't understand how the equation leading back to h/a=b/(x+y) proves that (x+h)^2+(y+h)^2=(a+b)^2.

gwenspooner85  Jul 6, 2020
edited by gwenspooner85  Jul 6, 2020