If y = acos(log (x)) + bsin (log(x)), where a, b are parameters, then xy" + xy' is equal to
y
- y
2y
- 2y
The two curves x = y2, xy = a2 cut orthogonally at a point, then a2 is equal to
1
2
B.
If u(x, y) = ylog(x) + xlog(y), then
uxuy - uxlog(x) - uylog(y) + log(x)log(y) is equal to
0
- 1
1
2