<h3>
Answer:</h3>
11. {OD, OH} . . . or . . . {OB, OJ}
12. b. Open a compass to distance AB
13. 17 square units
<h3>
Step-by-step explanation:</h3>
11. Opposite rays are rays that together make a line. The only point they have in common is their mutual end point.
Given the letter names of points on lines, one can name opposite rays by choosing 3 collinear points, and selecting the middle one of those for the mutual end point. That point's name will be the first letter of each of the ray names. One ray will be named by one of the remaining points, and the other will be named by the other remaining point.
Here, we can choose points H, O, D on the same line. Then rays in opposite directions will be OD and OH, each having point O as its end point.
Similarly, we can choose points B, O, J on the other line and name opposite rays OB and OJ.
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12. The general sequence of steps for copying a line segment is to draw a line segment longer than the one you want to copy, mark a point on it, set the compass to the length of the given segment, then use the marked point as one end and mark the distance from that point using the compass.
Here, the target line and reference point (C) have been made already, so the next step is <em>open the compass to distance AB</em>.
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13. The unadulterated triangle has legs of 6 and 8 units, so an area of ...
... area = (1/2)bh = (1/2)(6)(8) = 24 . . . . square units.
One can count the squares within that area that have been removed from the triangle. There are 7 of them, so the area is ...
... 24 -7 = 17 . . . . square units
There are other ways to find the area, including dividing the triangle into smaller pieces. Doing the latter, one needs to be careful, because the slanted side only goes through a grid intersection at points (1, 1), (4, 5), and (7, 9).
If one uses two triangles with legs 3 and 4, and a central rectangle of 2×3, then the area adds up to 6+6+5 = 17 square units, because there is one square taken out of the lower right corner of the upper triangle.
