Задача 27805 113...

vk232428545

21.05.2018

113

SOVA

21.05.2018

★

S= ∫ _( альфа )^( бета ) (r^2/2)d phi

S= ∫ _(-Pi)^(Pi)(3*(1+cos phi ))^2d phi =

=2 ∫ _(0)^(Pi)9*(1+2cos phi +cos^2 phi )d phi =

=18∫ _(0)^(Pi)(1+2cos phi +(1+cos2phi)/2 )d phi =

=18*((3/2) phi +2sin phi +(1/2)sin2 phi )|_(0)^(Pi)=

=18*(3/2)*Pi=27Pi