In the x-y plane, the area of the region bounded by |x + y| < 20 an...
The condition |x + y| < 20 represents the region between two parallel lines that are symmetric about the x-axis. The inequality can be rewritten as -20 < x + y < 20.
We can break down this inequality into two separate inequalities:
x + y < 20
-(x + y) < 20
For the first inequality, x + y < 20, the region is below the line y = -x + 20.
For the second inequality, -(x + y) < 20, we multiply both sides by -1 to change the direction of the inequality, which gives us x + y > -20. The region for this inequality is above the line y = -x - 20.
Combining these two regions, we have a trapezoidal shape with two parallel sides: y = -x + 20 and y = -x - 20.
Now, we need to find the intersection points of these lines with the line y = 20 (0 < y < 20) to determine the boundaries of our trapezoid.
For y = 20:
-20 = -x + 20 => x = 0
-20 = -x - 20 => x = 0
So, the trapezoid is symmetric about the y-axis and its base has a length of 2x, where x = 20.
The formula for the area of a trapezoid is:
Area = (a + b) * h / 2
In this case, a = b = 2x = 40 and h = 20. Plugging in these values, we get:
Area = (40 + 40) * 20 / 2
= 80 * 20 / 2
= 1600 / 2
= 800
Therefore, the area of the region bounded by |x + y| < 20 and 0 < y < 20 is 800. So the answer is B.