Answer:
20) ![\displaystyle [4, 1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B4%2C%201%5D)
19) ![\displaystyle [-5, 1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-5%2C%201%5D)
18) ![\displaystyle [3, 2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B3%2C%202%5D)
17) ![\displaystyle [-2, 1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-2%2C%201%5D)
16) ![\displaystyle [7, 6]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B7%2C%206%5D)
15) ![\displaystyle [-3, 2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-3%2C%202%5D)
14) ![\displaystyle [-3, -2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-3%2C%20-2%5D)
13) ![\displaystyle NO\:SOLUTION](https://tex.z-dn.net/?f=%5Cdisplaystyle%20NO%5C%3ASOLUTION)
12) ![\displaystyle [-4, -1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-4%2C%20-1%5D)
11) ![\displaystyle [7, -2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B7%2C%20-2%5D)
Step-by-step explanation:
20) {−2x - y = −9
{5x - 2y = 18
⅖[5x - 2y = 18]
{−2x - y = −9
{2x - ⅘y = 7⅕ >> New Equation
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![\displaystyle \frac{-1\frac{4}{5}y}{-1\frac{4}{5}} = \frac{-1\frac{4}{5}}{-1\frac{4}{5}}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B-1%5Cfrac%7B4%7D%7B5%7Dy%7D%7B-1%5Cfrac%7B4%7D%7B5%7D%7D%20%3D%20%5Cfrac%7B-1%5Cfrac%7B4%7D%7B5%7D%7D%7B-1%5Cfrac%7B4%7D%7B5%7D%7D)
[Plug this back into both equations above to get the x-coordinate of 4]; ![\displaystyle 4 = x](https://tex.z-dn.net/?f=%5Cdisplaystyle%204%20%3D%20x)
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19) {−5x - 8y = 17
{2x - 7y = −17
−⅞[−5x - 8y = 17]
{4⅜x + 7y = −14⅞ >> New Equation
{2x - 7y = −17
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![\displaystyle \frac{6\frac{3}{8}x}{6\frac{3}{8}} = \frac{-31\frac{7}{8}}{6\frac{3}{8}}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B6%5Cfrac%7B3%7D%7B8%7Dx%7D%7B6%5Cfrac%7B3%7D%7B8%7D%7D%20%3D%20%5Cfrac%7B-31%5Cfrac%7B7%7D%7B8%7D%7D%7B6%5Cfrac%7B3%7D%7B8%7D%7D)
[Plug this back into both equations above to get the y-coordinate of 1]; ![\displaystyle 1 = y](https://tex.z-dn.net/?f=%5Cdisplaystyle%201%20%3D%20y)
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18) {−2x + 6y = 6
{−7x + 8y = −5
−¾[−7x + 8y = −5]
{−2x + 6y = 6
{5¼x - 6y = 3¾ >> New Equation
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![\displaystyle \frac{3\frac{1}{4}x}{3\frac{1}{4}} = \frac{9\frac{3}{4}}{3\frac{1}{4}}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B3%5Cfrac%7B1%7D%7B4%7Dx%7D%7B3%5Cfrac%7B1%7D%7B4%7D%7D%20%3D%20%5Cfrac%7B9%5Cfrac%7B3%7D%7B4%7D%7D%7B3%5Cfrac%7B1%7D%7B4%7D%7D)
[Plug this back into both equations above to get the y-coordinate of 2]; ![\displaystyle 2 = y](https://tex.z-dn.net/?f=%5Cdisplaystyle%202%20%3D%20y)
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17) {−3x - 4y = 2
{3x + 3y = −3
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![\displaystyle \frac{-y}{-1} = \frac{-1}{-1}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B-y%7D%7B-1%7D%20%3D%20%5Cfrac%7B-1%7D%7B-1%7D)
[Plug this back into both equations above to get the x-coordinate of −2]; ![\displaystyle -2 = x](https://tex.z-dn.net/?f=%5Cdisplaystyle%20-2%20%3D%20x)
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16) {2x + y = 20
{6x - 5y = 12
−⅓[6x - 5y = 12]
{2x + y = 20
{−2x + 1⅔y = −4 >> New Equation
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![\displaystyle \frac{2\frac{2}{3}y}{2\frac{2}{3}} = \frac{16}{2\frac{2}{3}}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B2%5Cfrac%7B2%7D%7B3%7Dy%7D%7B2%5Cfrac%7B2%7D%7B3%7D%7D%20%3D%20%5Cfrac%7B16%7D%7B2%5Cfrac%7B2%7D%7B3%7D%7D)
[Plug this back into both equations above to get the x-coordinate of 7]; ![\displaystyle 7 = x](https://tex.z-dn.net/?f=%5Cdisplaystyle%207%20%3D%20x)
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15) {6x + 6y = −6
{5x + y = −13
−⅚[6x + 6y = −6]
{−5x - 5y = 5 >> New Equation
{5x + y = −13
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![\displaystyle \frac{-4y}{-4} = \frac{-8}{-4}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B-4y%7D%7B-4%7D%20%3D%20%5Cfrac%7B-8%7D%7B-4%7D)
[Plug this back into both equations above to get the x-coordinate of −3]; ![\displaystyle -3 = x](https://tex.z-dn.net/?f=%5Cdisplaystyle%20-3%20%3D%20x)
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14) {−3x + 3y = 3
{−5x + y = 13
−⅓[−3x + 3y = 3]
{x - y = −1 >> New Equation
{−5x + y = 13
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![\displaystyle \frac{-4x}{-4} = \frac{12}{-4}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B-4x%7D%7B-4%7D%20%3D%20%5Cfrac%7B12%7D%7B-4%7D)
[Plug this back into both equations above to get the y-coordinate of −2]; ![\displaystyle -2 = y](https://tex.z-dn.net/?f=%5Cdisplaystyle%20-2%20%3D%20y)
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13) {−3x + 3y = 4
{−x + y = 3
−⅓[−3x + 3y = 4]
{x - y = −1⅓ >> New Equation
{−x + y = 3
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![\displaystyle 1\frac{2}{3} ≠ 0; NO\:SOLUTION](https://tex.z-dn.net/?f=%5Cdisplaystyle%201%5Cfrac%7B2%7D%7B3%7D%20%E2%89%A0%200%3B%20NO%5C%3ASOLUTION)
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12) {−3x - 8y = 20
{−5x + y = 19
⅛[−3x - 8y = 20]
{−⅜x - y = 2½ >> New Equation
{−5x + y = 19
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![\displaystyle \frac{-5\frac{3}{8}x}{-5\frac{3}{8}} = \frac{21\frac{1}{2}}{-5\frac{3}{8}}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B-5%5Cfrac%7B3%7D%7B8%7Dx%7D%7B-5%5Cfrac%7B3%7D%7B8%7D%7D%20%3D%20%5Cfrac%7B21%5Cfrac%7B1%7D%7B2%7D%7D%7B-5%5Cfrac%7B3%7D%7B8%7D%7D)
[Plug this back into both equations above to get the y-coordinate of −1]; ![\displaystyle -1 = y](https://tex.z-dn.net/?f=%5Cdisplaystyle%20-1%20%3D%20y)
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11) {x + 3y = 1
{−3x - 3y = −15
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![\displaystyle \frac{-2x}{-2} = \frac{-14}{-2}](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Cfrac%7B-2x%7D%7B-2%7D%20%3D%20%5Cfrac%7B-14%7D%7B-2%7D)
[Plug this back into both equations above to get the y-coordinate of −2]; ![\displaystyle -2 = y](https://tex.z-dn.net/?f=%5Cdisplaystyle%20-2%20%3D%20y)
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