5. (8 points)Let f(x,y) = ln(16-x- y2) (a) Find the domain of the function. Graph the domain of the function in R R. (b) Describe the level curves. 6. (10 points) Let f(x, y, z) = cosxy + e + Inzx and the point P (1,0,1) Find the directional derivative of f at (1,0,1) in the direction of v = i +2j+2k f(x14, 2) = cosxy + ex + Inzx y, 1x = cos x + 1 Z e Jy = cos y + e cosy 2 1 12 = c + 4 X 6. (1,2, Du | (1,0,1) = (cos y + 1 )1 + (cos + + e ) 2 + (e = COSO + 1 2 2 2 + (cos 1 + e 12 ) 2 + ( 8 2 + + (cos 1 + 1/2) 2 1 + 2 e 7 + (cos 1 + e (cos 1 + e 1/2) 2 7 & 20 1/2 2e +