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In Exercises 43-52, sketch the level curves c = -3, -2, -1, 0, 1, 2, 3 if they exist for the specified function. 3x 43. f( x, y) = x+y 44. f (x, y) = y 3x 45. f (x, y) = y2 46. f(x, y) = xy 47. f (x, y) = 4 - (x2+ yz) 48. f (x, y) = x2 - 12 49. f(x, y) = sin(x + !) 50. f (x, y) = cos(xy) 51. f(x, y) = yescx 52. f (x, 1/) = 1/ secx