I think that is the correct formula. What is the problem? I get . Gives an arc length of , which looks plausible.
Consider the parametric equation
x=4(cos+sin)
y=4(sin–cos)
What is the length of the curve for =0 to =9pi/10
the formula i believe is
L=integral from t0 to t1 sqrt((dx/dt)^2+(dy/dt)^2)dt
ive tried pluggin in the derivatives of of x and y for dx dt and integrating from 0 to 9pi/10 but its not working