Question

Help, please????????

Answer 1

9514 1404 393

Answer:

  E)  25.5 units²

Step-by-step explanation:

The figure is not carefully drawn, so it is difficult to tell that it is a trapezoid. The "height" of it is BC, the diagonal of a rectangle that is 1 unit by 4 units. The Pythagorean theorem tells you that length is ...

  BC = √(1² +4²) = √17

We notice that the "bases" of the trapezoid (CD and AB) are 1 and 2 times this length. The trapezoid area formula tells us the area is ...

  A = 1/2(b1 +b2)h

  A = 1/2((√17)(1 +2))(√17) = 3/2(17) = 25.5 . . . . square units

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Alternate solution

Pick's Theorem is a theorem that can help you find the area of a polygon when its vertices are all on grid points. It tells you the area is ...

  A = i + b/2 -1

where i is the number of grid points interior to the figure, and b is the number of grid points on the boundary. Here, the boundary grid points are those that are labeled plus the one at (-2, 1). Counting the interior grid points gives a total of 24, so the area by Pick's theorem is ...

  A = 24 + 5/2 -1 = 25.5 . . . square units

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Additional comment

Once you're familiar with Pick's theorem (and/or any of a few other methods of computing area from coordinates), you see that the area of any polygon whose vertices are grid points will be an integer multiple of 1/2. The only such answer choice here is choice E.