Your thinking is right, it is just tricky wording. You would only need two angles if you knew that 1 was along line 'N' and one was on line 'O'. However, to be certain that you have one along each line, you would need to have 9 angles. The first 8 could be on 1 line and then the 9th would be on the other. Hope that helps.

hi jim,
still unable to understand .

if i have one angle on one line, then i will know other angles that are formed by that line.

same way y cannot i assume one angle on the other line and come to know all the angles out there.


so in all i just need two angles...

i know i am wrong obviously but still unable to get the concept

If you assigned the angles labels of 1-16, 1-8 would be on one line and 9-16 would be on the other. Thus, if you randomly picked angles you could pick 1-8 first and only know all of the angles on one line. The 9th will make sure you have at least one angle from each line. The angle concept you have just think about the randomness in the selection as described above.

let me rephrase to you ..

(THERE ARE TWO NON PARALLEL LINES N and O)

1. how we can be sure, the two angles given to you are along two different lines,
2. suppose the given angles are along the same line, how can we find an angle, which along the other line
3. now, suppose we are given 8 angles, but those angles could be across the same line,
4. so to guarantee that all 16 angles could be determined, we need atleast one angle along the both lines
and that can be guaranteed only if we are given with 9 angles (supposing 8 angles are along one line and 1 angle is along the other line)

i hope it clarifies

[/img]