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elena55 [62]
3 years ago
5

When solving the equation x2 – 8x - 7 = 0 by completing the square, which equation

Mathematics
1 answer:
IgorLugansk [536]3 years ago
4 0
<h3><u>A</u><u>n</u><u>s</u><u>w</u><u>e</u><u>r</u><u>:</u><u>-</u></h3>

Lets Solve

\\  \rm \longmapsto \:  {x}^{2}  - 8x - 7 = 0 \\  \\  \rm \longmapsto \:  {x}^{2}  - 8 {}^{}x = 7 \\  \\  \rm \longmapsto \: 4( {x}^{2}  - 8x) = 4 \times 7 \\  \\  \rm \longmapsto \:  {4x}^{2}  - 32x = 28 \\  \\  \rm \longmapsto \:  {(2x)}^{2}  - 2 \times 2x \times 8 = 28 \\  \\  \rm \longmapsto \: (2x) {}^{2}  - 2 \times 2x \times 8 +  {8}^{2}  = 28 +  {8}^{2}  \\  \\  \rm \longmapsto \:  {(2x - 8)}^{2}  = 64 + 28 \\  \\  \rm \longmapsto \:  {(2x - 8)}^{2}  = 92 \\  \\  \rm \longmapsto \: 2x - 8 =  \underline{ + }9.3 \\ \\  \rm \longmapsto \:2x =  8 + 9.3  \: or \: 8 - 9.3 \\ \\  \rm \longmapsto \:2x = 17.3 \:or \:  - 1.3 \\ \\  \rm \longmapsto \:2x = 17.3 \\ \\  \rm \longmapsto \:x =  \frac{17.3}{2}  \\ \\  \rm \longmapsto x = \:8.6

  • Ignore negative value
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tia_tia [17]

Answer: You are incorrect, the slope is correct, but the actual y-intercept is 205 ft.

Then the equation is:

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Step-by-step explanation:

Ok, let's solve this.

We know that water is drained from a reservoir, let's assume that we can model this situation with a linear relation:

y = a*x + b

Where x is time, y is the height of the water in the reservoir, a is the slope (in this case represents how much changes the height of the water in the reservoir in one unit of time) and b is the initial height of the water in the reservoir.

We know that for a line that passes through the points (x₁, y₁) and (x₂, y₂) the slope is:

a = (y₂ - y₁)/(x₂ - x₁)

For this particular case we know that after 2 minutes the height of the water is 175 ft, then we have the point (2 min, 175 ft)

and after 5 minutes (so 7 minutes in total), the height of the water is 100ft, then: (7 ft, 100ft)

Then the slope of this:

a = (100 ft - 175 ft)/(7 min - 2 min) = (-75ft/5min) = - 15 ft/min

Then our line is something like:

y = (-15ft/min)*x + b

To find the value of b, we can use the fact that when x = 2 min, y = 175 ft

So if we replace these two values in the equation we get:

175ft = (-15 ft/min)*2 min + b

175 ft = -30 ft + b

175 ft + 30 ft = b                  

(here is your problem, it seems like you subtracted instead of adding in this part)

205 ft = b

Then the equation is:

y = (-15 ft/min)*x + 205 ft

So you are incorrect (but only for a little bit), you computed wrong the y-intercept.

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Step-by-step explanation:

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Step-by-step explanation:

Given polynomials are:

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Keywords: Polynomials, Multiplication

Learn more about polynomials at:

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