This is in Differential Calculus. This is only multiple choice. Provide necessary solution for each items. Thank you and Godbless.

10. If = = xsiny + ycosx, find the total differential d=. A) (siny -ysix)dx - (x cosy + cosx)dy C) (siny + ysinx)dx + (xcosy - cosx)dy B) (siny + y sinx )dx + (x cosy + cosx)dy D) (siny -ysinx )dx + (x cosy + cosx)dy 11. The sum of three positive numbers is 30. Find the largest number if the product of the first number, the square of the second number and the cube of the third number is maximum? A) 18 C) 12 B) 15 D) 10 12. Evaluate lim x -six xSIX A) ON C) -1 B) D) 1