1. x-y=1 x+y=-5
2. x-4y=10
2x+y=2
3. -5x+y=0
x+y=6
4. y=6-2x
y=4
5. 2y=16
4x-y= 4
6. x=y -4
3x+y=12
7. y- 2x=-6
5x-y= 9
8. 3y+x= 2
y-x=-6

Statements reasons 1. ab ? cd; ad ? bc 1. given 2. ac ? ac 2. reflexive property 3. ? adc ? ? cba 3. ? 4. ? dac ? ? bca; ? acd ? ? cab 4. cpctc 5. ? dac and ? bca are alt. int. ? s; ? acd and ? cab are alt. int. ? s 5. definition of alternate interior angles 6. ab ? cd; ad ? bc 6. converse of the alternate interior angles theorem 7. abcd is a parallelogram 7. definition of parallelogram what is the missing reason in step 3?