07/11/18 23:04:54 0
>>539
dS = (xdy-ydx)/2
= (3/2)a^2･{cos(t)}^4･{sin(t)}^2･dt + (3/2)a^2･{sin(t)}^4･{cos(t)}^2･dt
= (3/2)a^2･{cos(t)sin(t)}^2･dt
= (3/8)a^2･{sin(2t)}^2･dt
= (3/16)a^2･{1-cos(4t)}dt,
0≦t≦π/2 で積分すると sin(4t)の項は0になるので S/4 = (3π/32)a^2,
S = (3π/8)a^2,
これでおＫ？