Posted by **Geometry** on Tuesday, August 18, 2009 at 7:22pm.

h t t p : / / i m g 3 5 . i m a g e s h a c k . u s / i m g 3 5 / 8 0 8 7 / 4 7 2 4 1 4 6 9 . j p g

my book says

if a1 is perpendicular to a2 and b1 is perpeindicular to b2 then angle one equal angle two

WHY????

Also I remeber it was very simple but don't remeber why... if we exten lines a2 and b2 then angle two equals angle 3

WHY???

Please provide me with the reasons...

Thanks

- Geometry -
**Reiny**, Tuesday, August 18, 2009 at 7:32pm
I see two right-angled triangles in which opposite angles are also equal.

So if two angles of one triangle are equal to two angles of another triangle then the third angle pair must also be equal.

"sum of angles in a triangle theorem"

- QUESTION -
**QUESTION**, Tuesday, August 18, 2009 at 7:46pm
what are these opposite angles that you are making reference to sorry it's been a while sense I took geometry

- Geometry -
**Reiny**, Tuesday, August 18, 2009 at 7:49pm
draw any two intersecting straight lines.

Do you see two pairs of opposing or "opposite" angles?

Aren't they equal ?

- Geometry -
**bobpursley**, Tuesday, August 18, 2009 at 7:56pm
Opposite angles are equal because each of those angles is supplementary to a common angle.

A+B=180

A+C=180

B must =C

- QUESTION -
**QUESTION**, Tuesday, August 18, 2009 at 8:08pm
oh and also what makes angle three equal to angle to if you extended the lines

- Geometry -
**bobpursley**, Tuesday, August 18, 2009 at 8:19pm
Those will be opposite angles (if two lines intersect, then opposite angles are equal)

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