Find an equation for the line tangent to the curve at the point defined by the given value of t. Also, find the value of d2y dx2 at this point. x = 4 sint, y = 2 cost, t = π4 The equation represents the line tangent to the curve at t = π4. (Type an exact answer, using radicals as needed. ) The value of d2y dx2 at t = π4 is (Type an exact answer, using radicals as needed. )