<span>arccos (cos 4 pi/3)=arccos(cos(</span>π+π/3))=arccos(-cosπ/3)=-π/3
S=a*b/2 где а и b катеты
c^2=a^2+b^2
a=16 c=34
b=из под корня(34^2-16^2)=30
S=30*16/2=240
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(5у)^2 - (2х)^2= 25у^2 - 4х^2