y`_(t)=2Rcost-2Rcos2t
(x`_(t))^2=(-2Rsint+2Rsin2t)^2=4R^2sin^2t-8R^2sint*sin2t+4R^2sin^22t
(y`_(t))^2=(2Rcost-2Rcos2t)^2=4R^2cos^2t-8R^2cos*cos2t+4R^2cos^22t
[b](x`_(t))^2+(y`_(t))^2=[/b] 4R^2*([b]sin^2t+cos^2t[/b])+4R^2*([b]sin^22t+cos^22t[/b])+
-8R^2*(sint*sin2t+cost*cos2t)=8R^2*(1-cost)=8R^2*2sin^2(t/2)=[red]16R^2sin^2(t/2)[/red]
[b]sin^2t+cos^2t[/b]=1
[b]sin^22t+cos^22t[/b]=1
cost*cos2t+sintsin2t=cos(2t-t)=cost
sqrt((x`_(t))^2+(y`_(t))^2)=[red]4R*sin(t/2)[/red]
S=2π ∫ ^(2π)_(0)(2Rsint-Rsin2t)4R*sin(t/2) dt=
=2π ∫ ^(2π)_(0)2Rsint*4R*sin(t/2) dt-2π ∫ ^(2π)_(0)Rsin2t*4R*sin(t/2) dt=
=16πR^2 ∫ ^(2π)_(0)sint*sin(t/2) dt-8πR^2 ∫ ^(2π)_(0)sin2t*sin(t/2) dt=...
Применяем формулы
sin α *sin β =