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Maths - Circle Theorems Help - Prove angle x is equal to y-180 watch

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1. Below is a picture. I want to know how you can prove that x or Angle CAB is equal to y-180 or angle CDB
2. There is the picture. HELP! P.S: Clicking on it makes it bigger.
3. Just to be sure, was it stated that CD is a tangent to the circle?
4. (Original post by justinawe)
Just to be sure, was it stated that CD is a tangent to the circle?
Yes
5. Ok then, these are the things you should note:

Angle CDB is 180-y degrees. as triangle BCD is an isosceles triangle, angle BCD will be the same.

given that CD is a tangent to the circle, then what is angle ACD? using this and 180-y for angle BCD, you can find angle ACB.

as triangle ABC is in a semi-circle, what does this make angle ABC?

With this info you should be able to show that x = 180-y
6. I still can't work it out
7. (Original post by justinawe)
Ok then, these are the things you should note:

Angle CDB is 180-y degrees. as triangle BCD is an isosceles triangle, angle BCD will be the same.

given that CD is a tangent to the circle, then what is angle ACD? using this and 180-y for angle BCD, you can find angle ACB.

as triangle ABC is in a semi-circle, what does this make angle ABC?

With this info you should be able to show that x = 180-y
...
8. (Original post by justinawe)
Ok then, these are the things you should note:

Angle CDB is 180-y degrees. as triangle BCD is an isosceles triangle, angle BCD will be the same.

given that CD is a tangent to the circle, then what is angle ACD? using this and 180-y for angle BCD, you can find angle ACB.

as triangle ABC is in a semi-circle, what does this make angle ABC?

With this info you should be able to show that x = 180-y
...
9. Use the alternate segment theorem: the angle between a tangent and a chord at the point of contact is equal to the angle subtended by the chord.
10. Thanks

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Updated: November 5, 2015
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