x=var('x')
y=var('y')
x=cos(t)
y=sin(t)
f1=y*y-7*y
f2=2*x*y+2*x
y1=diff(y,t,1)
x1=diff(x,t,1)
f1=x*y1
f2=y*x1
c=f1-f2
d=integrate(c,(t,0,2*pi))