Book I. Propositions 9 and 10
Back to Propositions 9 and 10.
1. Draw an angle, and bisect it.
2. a) In Proposition 9, what are we given?
To see the answer, pass your mouse over the colored area.
2. b) What are we required to do?
2. c) Practice Proposition 9.
3. Use Proposition 9 to prove: In an isosceles triangle the angles at the base are
Let ABC be an isosceles triangle with AB equal to AC. Then angle ABC is equal to angle ACB
Bisect angle BAC with the straight line AD.
Then, since BA is equal to CA, and AD is common to the two triangles ADB, ADC,
therefore angle ABD is equal to angle ACD.
4. Draw a straight line, and bisect it.
5. a) In Proposition 10, what are we given?
A straight line.
4. b) What are we required to do?
5. c) Practice Proposition 10.
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