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patriot [66]
3 years ago
13

you have a 5-inch by 7-inch picture that you framed. When you hung the picture, you found that the entire area is 69.56 in. What

is the width of the frame?​

Mathematics
2 answers:
riadik2000 [5.3K]3 years ago
8 0

Answer:  d) 2.4 inches

<u>Step-by-step explanation:</u>

Let x represent the width of the frame

Then the area of the frame is:

(x + 5)(x + 7) = 69.56

Rewrite it in Standard form of a quadratic equation:

x² + 12x + 35 = 69.56

x² + 12x - 34.56 = 0

Use Quadratic Formula to solve for x:

x=\dfrac{-b+\sqrt{b^2-4ac}}{2a}\\\\\\x=\dfrac{-12+\sqrt{12^2-4(1)(-34.56)}}{2(1)}\\\\\\x=\dfrac{-12+\sqrt{282.24}}{2}\\\\\\x=\dfrac{-12+16.6}{2}\\\\\\x=\dfrac{4.8}{2}\\\\\\x=\large\boxed{2.4}

Montano1993 [528]3 years ago
4 0

Answer:

d. 2.4 in

Step-by-step explanation:

So initially w/o frame the area was 5 x 7 = 35 sq in.

Now we have to add the width of the frame to both dimensions.

(5+w)(7+w) = 69.56 sq in

35 + 7w + 5w + w² = 69.56

w² + 12w + 35 = 69.56

w² + 12w - 34.56 = 0

I use the quadratic formula to solve this (x = -b±√b²-4ac / 2a). I cheat by using a quadratic program on the calculator :,)

w = 2.4

w = -14.4

Since we can't have a negative width, the answer must be <u>w = 2.4 inches.</u>

You can also just plug the answer choices one-by-one into the calculator with guess-and-check because this is multiple choice.

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Let x, y, and z denote the side lengths of the box, with the bottom face having dimensions x-by-y and z is the height. Naturally this means each of x, y, and z must be greater than 0.

The box has a fixed volume of 252 cm³, so

xyz = 252

The surface area of the box is

2xy + 2xz + 2yz

and we're told that the material cost for each face is different. The total cost of the material needed to make the box is given by

C (x, y, z) = ($5/cm²) xy + ($2/cm²) xy + 2 ($3/cm²) (xz + yz)

or, omitting units and simplifying,

C (x, y, z) = 7xy + 6 (x + y) z

In the volume constraint, solve for any one variable; I'll do z.

z = 252/(xy)

Substitute this into the cost function:

C (x, y, 252/(xy)) = 7xy + 1512 (x + y)/(xy)

Since this is now a function of 2 variables, I'll rewrite this as

C* (x, y) = 7xy + 1512 (1/y + 1/x)

Compute the partial derivatives of C and find the critical points:

∂C/∂x = 7y - 1512/x² = 0   ⇒   x² y = 216

∂C/∂y = 7x - 1512/y² = 0   ⇒   x y² = 216

It follows that

x² y = x y²   ⇒   x = y

Just like before, we can think about C* as yet another function but only of 1 variable,

C** (x) = 7x² + 3024/x

Now find the critical points of C** :

dC**/dx = 14x - 3024/x² = 0   ⇒   x = 6

All of this tells us that C (x, y, z) has a critical point when x = y = 6 and z = 252/6² = 7. So the box that costs the least has dimensions 6 × 6 × 7 cm, which gives the box a surface area of 240 cm² and a total cost of $756.

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2 years ago
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nadya68 [22]

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7 0
3 years ago
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pav-90 [236]

Answer with positive exponent = \left(\frac{1}{5}\right)^3 or  \frac{1}{5^3}

Answer with negative exponent = 5^{-3}

===========================================================

Explanation:

The rule we use is

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If we multiply two exponential expressions with the same base, then we add the exponents.

The base for each is 5. The exponents 4 and -7 add to -3.

This means

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To convert to a positive exponent, we apply the reciprocal to the base. We go from 5, aka 5/1, to 1/5.

So, 5^{-3} = \left(\frac{1}{5}\right)^3 = \frac{1^3}{5^3} = \frac{1}{5^3}

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