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2 years ago

Item 8 Solve for x. Use the quadratic formula. 2x2−5x−9=0 Enter the solutions, in simplified radical form, in the boxes.

Mathematics

2 answers:

Lubov Fominskaja [6]2 years ago

7 0

Answer:

5+√97/4

Also 5-√97/4

Step-by-step explanation:

The Quadratic formula is x=-b+-√b^2-4ac/2a

This means that we should plug the values for A B AND C into the formula

We can work out that

A = 2

B=-5

C=-9

Once we have put these into the formula we get

5+√97/4 (all over 4) aka 3.71

Also 5-√97/4 (all over 4) aka -1.21

Dimas [21]2 years ago

3 0

Answer:

$\large\boxed{x=\dfrac{5-\sqrt{97}}{4}\ or\ x=\dfrac{5+\sqrt{97}}{4}}$

Step-by-step explanation:

$\text{Let}\ ax^2+bx+c=0\\\\\text{The quadratic formula:}\\\\\Delta=b^2-4ac\\\\\text{If}\ \Delta>0,\ \text{then the equation has two solutions}\ x=\dfrac{-b\pm\sqrt\Delta}{2a}\\\\\text{If}\ \Delta=0,\ \text{then the equation has one solution}\ x=\dfrac{-b}{2a}\\\\\text{If}\ \Delta$

$\text{The equation}\ 2x^2-5x-9=0\\\\a=2,\ b=-5,\ c=-9\\\\\Delta=(-5)^2-4(2)(-9)=25+72=97>0\\\\\sqrt\Delta=\sqrt{97}\\\\x_1=\dfrac{-(-5)-\sqrt{97}}{2(2)}=\dfrac{5-\sqrt{97}}{4}\\\\x_2=\dfrac{-(-5)+\sqrt{97}}{2(2)}=\dfrac{5+\sqrt{97}}{4}$

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The original quantity is 20 and the new quantity is 15. Adam incorrectly says the percent decrease is about 14.29%. What is the

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Answer: A. divided the difference of the two quantities by the sum of the two quantities.

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

Explanation:

The difference of the quantities is 20-15 = 5

The sum of the quantities is 20+15 = 35

Dividing those results leads to 5/35 = 0.142857 which rounds to 0.1429

That converts to 14.29%

This is likely the path Adam took. This path is incorrect. The correct steps are shown below

---------------------

Difference = 20-15 = 5

Divide the difference over the original quantity

5/20 = 1/4 = 0.25 = 25%

We have a 25% decrease because the new quantity (15) is smaller than the old quantity (20)

----------------------

Here's another way to approach the problem

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B = new value = 15

C = percent change

C = [ (B-A)/A ] * 100%

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The negative C value means we have a negative percent change, ie we have a percent decrease. So this is another way to get a 25% decrease.

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