1.8, Problem 37: A lidless cardboard box is to be made with a volume of 4 m3
. Find the
dimensions of the box that requires the least amount of cardboard.
Solution: If the dimensions of our box are x, y, and z, then we’re seeking to minimize
A(x, y, z) = xy + 2xz + 2yz subject to the constraint that xyz = 4. Our first step is to make
the first function a function of just 2 variables. From xyz = 4, we see z = 4/xy, and if we substitute
this into A(x, y, z), we obtain a new function A(x, y) = xy + 8/y + 8/x. Since we’re optimizing
something, we want to calculate the critical points, which occur when Ax = Ay = 0 or either Ax
or Ay is undefined. If Ax or Ay is undefined, then x = 0 or y = 0, which means xyz = 4 can’t
hold. So, we calculate when Ax = 0 = Ay. Ax = y − 8/x2 = 0 and Ay = x − 8/y2 = 0. From
these, we obtain x
2y = 8 = xy2
. This forces x = y = 2, which forces z = 1. Calculating second
derivatives and applying the second derivative test, we see that (x, y) = (2, 2) is a local minimum
for A(x, y). To show it’s an absolute minimum, first notice that A(x, y) is defined for all choices
of x and y that are positive (if x and y are arbitrarily large, you can still make z REALLY small
so that xyz = 4 still). Therefore, the domain is NOT a closed and bounded region (it’s neither
closed nor bounded), so you can’t apply the Extreme Value Theorem. However, you can salvage
something: observe what happens to A(x, y) as x → 0, as y → 0, as x → ∞, and y → ∞. In each
of these cases, at least one of the variables must go to ∞, meaning that A(x, y) goes to ∞. Thus,
moving away from (2, 2) forces A(x, y) to increase, and so (2, 2) is an absolute minimum for A(x, y).
Answer:
A.) -3
Step-by-step explanation:
-3 is less than -2 therefore, it fits the answer.
Answer: [D]: " 196π in.³ " .
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Explanation:
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Given: radius, "r", equal 7 in.
Given: height, "h", equals 4 in.
Volume: V = Base area * h ;
The base area of a cone is a circle: A = π * r² = π* (7²) = 49π .
(NOTE: Since all answer choices given are in terms of "π" ; we will leave the units in terms of "π").
V = (Based area) * h = (49π in.) * (4 in.) = (49*4)π in.³
= 196π in.³ ; which is: Answer choice: [D] .
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Answer:
Figure D
Step-by-step explanation:
we know that
If the scale factor of the dilation is 1/2, that means the dilation is a reduction
so
the answer is between the Figure C and Figure D
but
a rotation of 180° eliminate the Figure C
therefore
The answer is the Figure D
