Speak in English please. I would be more pleased to help if you write in English.
I’m not sure if the 15 is the question number but if it is the answer is 32. use PEMDAS
Answer: ![A^{-1}=\left[\begin{array}{cc}\frac{3}{2}&-\frac{1}{2}\\-2&1\end{array}\right]](https://tex.z-dn.net/?f=A%5E%7B-1%7D%3D%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D%5Cfrac%7B3%7D%7B2%7D%26-%5Cfrac%7B1%7D%7B2%7D%5C%5C-2%261%5Cend%7Barray%7D%5Cright%5D)
<u>Step-by-step explanation:</u>
![\left[\begin{array}{cc}2&1\\4&3\end{array}\right]=\left[\begin{array}{cc}1&0\\0&1\end{array}\right]](https://tex.z-dn.net/?f=%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D2%261%5C%5C4%263%5Cend%7Barray%7D%5Cright%5D%3D%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D1%260%5C%5C0%261%5Cend%7Barray%7D%5Cright%5D)
![\dfrac{1}{2}Row\ 1\rightarrow\left[\begin{array}{cc}1&\frac{1}{2}\\4&3\end{array}\right]=\left[\begin{array}{cc}\frac{1}{2}&0\\0&1\end{array}\right]](https://tex.z-dn.net/?f=%5Cdfrac%7B1%7D%7B2%7DRow%5C%201%5Crightarrow%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D1%26%5Cfrac%7B1%7D%7B2%7D%5C%5C4%263%5Cend%7Barray%7D%5Cright%5D%3D%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D%5Cfrac%7B1%7D%7B2%7D%260%5C%5C0%261%5Cend%7Barray%7D%5Cright%5D)
![Row\ 2 -4 \ Row\ 1\rightarrow \left[\begin{array}{cc}1&\frac{1}{2}\\0&1\end{array}\right]=\left[\begin{array}{cc}\frac{1}{2}&0\\-2&1\end{array}\right]](https://tex.z-dn.net/?f=Row%5C%202%20-4%20%5C%20Row%5C%201%5Crightarrow%20%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D1%26%5Cfrac%7B1%7D%7B2%7D%5C%5C0%261%5Cend%7Barray%7D%5Cright%5D%3D%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D%5Cfrac%7B1%7D%7B2%7D%260%5C%5C-2%261%5Cend%7Barray%7D%5Cright%5D)
![Row\ 1-\dfrac{1}{2}\ Row\ 2 \rightarrow \left[\begin{array}{cc}1&0\\0&1\end{array}\right]=\left[\begin{array}{cc}\frac{3}{2}&-\frac{1}{2}\\-2&1\end{array}\right]](https://tex.z-dn.net/?f=Row%5C%201-%5Cdfrac%7B1%7D%7B2%7D%5C%20Row%5C%202%20%5Crightarrow%20%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D1%260%5C%5C0%261%5Cend%7Barray%7D%5Cright%5D%3D%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D%5Cfrac%7B3%7D%7B2%7D%26-%5Cfrac%7B1%7D%7B2%7D%5C%5C-2%261%5Cend%7Barray%7D%5Cright%5D)
Direct variation mean x =ky so y = x/k
(2,14) mean y = kx so 14 = k*2 so 14 = 7*2 so 14 = 14
(4,28) mean y = kx so 28 = k*4 so 28 = 7*4 so 28 = 28
from these result that the 3rd choice is right sure
surface area (S) of a right rectangular solid is:
S = 2*L*W + 2*L*H + 2*W*H (equation 1)
where:
L = length
W = width
H = height
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you have:
L = 7
W = a
H = 4
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formula becomes:
S = 2*7*a + 2*7*4 + 2*a*4
simplify:
S = 14*a + 56 + 8*a
combine like terms:
S = 22*a + 56
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answer is:
S = 22*a + 56 (equation 2)
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to prove, substitute any value for a in equation 2:
let a = 15
S = 22*a + 56 (equation 2)
S = 22*15 + 56
S = 330 + 56
S = 386
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since a = 15, then W = 15 because W = a
go back to equation 1 and substitute 15 for W:
S = 2*L*W + 2*L*H + 2*W*H (equation 1)
where:
L = length
W = width
H = height
-----
you have:
L = 7
W = 15
H = 4
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equation 1 becomes:
S = 2*7*15 + 2*7*4 + 2*15*4
perform indicated operations:
S = 210 + 56 + 120
S = 386
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surface area is the same using both equations so:
equations are good.
formula for surface area of right rectangle in terms of a is:
S = 22*a + 56
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