The length of AB: 4*3= 12(dm) requires the radius and diameter of isosceles right triangle and circle.
Shaded area:
12 * 4-1/2 * 4 * 3.14 * 4 *1/2 total area-triangular area-semicircular area
=48-8-25. 12
= 14.88 (square decimeter)
2.
Connect two semicircles into a circle.
Shaded area:
10 *10-3.14 * 5 * 5 square area-circular area
= 100-78.5
=2 1.5 (square decimeter)
Shadow part perimeter:
10 * 2+3.14 *10 square upper and lower length+circular circumference
=20+3 1.4
=5 1.4 (decimeter)
As can be seen from the figure, the upper bottom of the trapezoid is equal to the diameter of the circle.
Shadow area:1/2 * (10+20) * 5-1/2 * 3.14 * 5 * 5 trapezoidal area-semicircular area.
=75-39.25
=35.75 (square decimeter)
TAT, Xiao Bai NC, don't steal = =+Sorry, I was stolen recently-=