Example on worksheet (subtracting by adding up)

50-29?

29+20=49

49+1=50

20+1=21

50-29=21

My question is where did the 20 come from? can you help me understand this?

(49 - 29) + 1 =(50 - 29)

Step-by-step explanation:

The 20 comes from the subtraction of 29 in both sides of the previous step equality. In the following, I transcript the complete procedure and I add the step that you need to understand why 20 appears (in bold numbers):

29+20=49

49+1=50

(49 - 29) + 1 =(50 - 29)

20+1=21

50-29=21

hence, it was only nesseraty to subtract 29

for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.