(a) F = (10xz + y2 ) i + 2xyj + 5x2k. curl F = F is a gradient field (b) G = (5xy + yz) i + ( 5x2 + z2 ) j+ xzk: curl G = is not a gradient field (c) H = 5yzi+ (5xz + z2 ) j + (5xy + 2yz) k: curl H = H is a gradient field