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