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question 3. Investigate whether the following functions have extreme values? If there is, specify the type and value f(x,y) = 3x2 + 1236 + 43/3 + 63.72 + 5 3 b. Given a metion of 2 variables of implicit form : z = f (x, y) = cos(x2y) + 93'\" :2 Write down all the rst derivatives! C. An upright box with a bottom and a lid made of thin cardboard with a volume of 5 12 liters. Determine the size and shape of the upright box so that the material area is minimum