38 If f(x,y) = 4x^2y + 3xy^2 then fxx is given by
a. 8y
b. 4x^2+6xy
c. 8xy+3y^2
d. 6x
e. 8x+6y
39 Find the critical point of the function f(x.y) = 4e^x - xe^y.
a. (0,0)
b. (ln 4, 0)
c. (0, ln 4)
d. There are no critical points
e. (e,0)
40 Suppose f(x,y) is a function such that fx(a,b) = 0, fy(a,b) = 0, fxx(a,b) = 9, fyy(a,b) = 4,
fxy(a,b) = 5. Then (a,b) is
a. saddle point
b. a relative minimum
c. a relative maximum
d. neither a relative maximum, relative minimum or saddle point
e. the test (involving D) is inconclusive