A cross-section is the shape that would be exposed when cutting straight through a 3-D object. for example, cutting horizontally through a regular cone would expose a circle.
an intersection is where 2 or more shapes (does not matter how many dimensions) overlap. for example, the point at which two lines overlap is the intersection. or the area that two overlapping circles share is the intersection.
Answer:
Perimeter is 17.07
Step-by-step explanation:
We know that DF = EF = 5 cm, since D and E are the midpoints of AC and AB, both of which are 10 cm in length.
We need to use the Pythagorean theorem to get the length of DE.

So the perimeter of DEF is 5 + 5 + 7.07 = 17.07
The answer is -8/15 because you need to cancel out the variables first
2/3 of 18 would be 12 if thats what youre asking. you would do 2/3 x 18