Question

Prove that the opposite angles of a parallelogram are congruent.

Answer 1

prove congruent triangles ABC and ADC... and then BAD and BCD

by proving congruency... you can show that corresponding angles in congruent triangles are equal

Answer 2

would i prove that by using the vertical angles therom?

Answer 3

can you plzz help meh cause i dont understand

Answer 4

What can you say about angle 3 and angle 4?

Answer 5

they are congruent?

Answer 6

@alexwee123 may you PLEASE help me on this 1 i only got 5 minutes to complete mi test

Answer 7

here
the sum of angle 3 and angle 4 is 180

Answer 8

http://www.proofwiki.org/wiki/Opposite_Sides_and_Angles_of_Parallelogram_are_Equal

Answer 9

the sum of any two adjacent angles in a parallelogram are equal, because the opposite sides are parallel

Answer 10

look at that site
i can try to explain it but since you have only 5 minutes left i cant :/

Answer 11

@telliott99 is that all of it?

Answer 12

Well, yeah
3 + 4 = 1 + 4
3 = 1

Answer 13

So its corresponding angles and then the sum of any two adjacent angles in a parallelogram are equal, because the opposite sides are parallel

Answer 14

The theorem is:
http://www.mathsisfun.com/geometry/parallel-lines.html
That's where you get what I said (you have to use the defn of supplementary)

Answer 15

So it is just defenition of supplementary angles and parallel lines thereom

Answer 16

@telliott99 is that the right answer?

Answer 17

Yes, draw a picture and go through step by step if you need to, but I think it is relatively obvious.

Answer 18

And what I said before:
3 + 4 = 1 + 4
3 = 1

Answer 19

What thereom/postulate is that?

Answer 20

I gave you a link for it.

Answer 21

Ok. So my answer is < 3 & < 4 = 180 degrees: Supplementary angles definiton.
Line BC and AD are congruent: parallel lines definition.?

Answer 22

@telliott99 Really i dont get this can you plzz just tell meh the answer

Answer 23

extend AB beyond B to F
extend BC beyond C to G

angle FBC = angle 3 by alternate angles with parallel lines
angle 4 = 180 - angle FBC by supplementary angles
so angle 4 = 180 - angle 3

Follow exactly the same logic connecting angle 4 and angle 1
3 + 4 = 180 = 1 + 4
3 = 1
QED

Answer 24

:).. Thank you soo much.. your a life saver!

Answer 25

yw. I'm a little fatigued myself.