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Can someone please explain to me the given question and proof? otherwise I might just have to end up dropping my maths course because unfortunately I'm not understanding anything from my teacher. I'm not really 'seeing' the concept, if that makes sense.

Regards,

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  • $\begingroup$ The line $DE$ splits the inner angle in half. You have to prove that it therefore splits the outer angle in half. Do you see what I mean? $\endgroup$ – Jack M Jan 31 '14 at 6:22
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The thing you might be tripped up on is the 180. The 180 comes from the 'line' DE, which is a straight angle, you know, a 180. And since 180 is a constant, subtracting either $\angle CBD$ or $\angle ABD$ you'll end up with the same number.

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  • $\begingroup$ so in these type of questions, I have to be on the look out for constants? $\endgroup$ – Sarah E. Jan 31 '14 at 6:19
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    $\begingroup$ Most definitely yes, because looking at it won't tell you for sure if they are equal (they might be off by a smidge unnoticed to the naked eye, technically). But if you have a value, you can treat it like a reference. There's a quote from one of my math books that says, "Geometry helps you understand the problem, algebra lets you solve the problem". $\endgroup$ – user123254 Jan 31 '14 at 6:24

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