# Thread: Prove lines are parallel

1. ## Prove lines are parallel

Can someone please help me with this problem? This is what I have but I am not sure that it is proof.

RT=12 and TD = 4 which makes RD=16
The ratio of RT to RD is 12
16
This is reduced to 3
4

RS= 9 and SC=3 which makes RC=12
The ratio of RS to RC is 9
12

This is reduced to 3
4

The ratio of RT to RD equals the ratio of RS to RC which makes the lines TS and DC parallel.

2. Originally Posted by sanee66
Can someone please help me with this problem? This is what I have but I am not sure that it is proof.

RT=12 and TD = 4 which makes RD=16
The ratio of RT to RD is 12
16
This is reduced to 3
4

RS= 9 and SC=3 which makes RC=12
The ratio of RS to RC is 9
12

This is reduced to 3
4

The ratio of RT to RD equals the ratio of RS to RC which makes the lines TS and DC parallel.
what was the original question?

3. ## prove lines are parallel

Prove that ST and CD are parallel was the original question.

4. Originally Posted by sanee66
Prove that ST and CD are parallel was the original question.
your method seems accurate. if we can prove that all sides of the two triangles are proportional then they are similar triangles and hence the lines in question are parallel

but since you are doing a proof, you have to state more clearly what you are doing. you can just say "because the ratios are the same they are parallel", you have to say why that is so.