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Prove that root 7 is irrational by the method of contradiction

Alchen [17]

Let assume that $\sqrt7$ is a rational number. Therefore it can be expressed as a fraction $\dfrac{a}{b}$ where $a,b\in\mathbb{Z}$ and $\text{gcd}(a,b)=1$ .

$\sqrt7=\dfrac{a}{b}\\\\7=\dfrac{a^2}{b^2}\\\\a^2=7b^2$

This means that $a^2$ is divisible by 7, and therefore also $a$ is divisible by 7.

So, $a=7k$ where $k\in\mathbb{Z}$

$(7k)^2=7b^2\\\\49k^2=7b^2\\\\7k^2=b^2$

Analogically to $a^2=7b^2$ ------- $b^2$ is divisible by 7 and therefore so is $b$ .

But if both numbers $a$ and $b$ are divisible by 7, then $\text{gcd}(a,b)=7$ which contradicts our earlier assumption that $\text{gcd}(a,b)=1$ .

Therefore $\sqrt7$ is an irrational number.

8 0

3 years ago

9. In a rhombus whose side measures 34 and the smaller angle is 42°. Find the length of the larger diagonal, to the nearest tent

Veseljchak [2.6K]

Answer:

63.5

Step-by-step explanation:

The diagonals of a rhombus bisect opposite angles.

The longer diagonal bisects the 42° angle

The larger angle of the rhombus is 180 - 42 = 138

Let x = the length of the longer diagonal

You know two sides and the included angle of a triangle.

Using the law of cosines we get

$x^{2} = 34^{2} + 34^{2} -2(34)(34) cos 138\\ = 1156 + 1156 - 2312 cos 138\\ = 4030.150837...\\x = \sqrt{4030.150837} = 63.48$ $x^{2} = 34^{2} + 34^{2} -2(34)(34)cos 138\\ = 1156 + 1156 - 2312 cos 138\\ = 4030.1508...\\ x = \sqrt{4030.1508} \\ = 63.48$ x^2 = 34^2 + 34^2 - 2(34)(34) cos 138

= 1156 + 1156 - 2312 c0s 138

= 4030.1508...

x = sq rt 4030.1508...

= 63.5

7 0

2 years ago

Please view picture. Also please tell mehow you got the answer

Cerrena [4.2K]

Have a look at the image attachment. I've added the points A, B, C, D such that
A = base of the diving board pole, or location of the pool deck
B = the location 1.6 meters directly above point A
C = location of the person's eyes
D = diving board location
The goal is to find the length of segment AD

We are given
AB = 1.6
BC = 3.67
what we want to find is
BD = x

Due to the fact we have similar right triangles ABC and CBD, we can form the proportion below and solve for x
AB/BC = BC/BD
1.6/3.67 = 3.67/x
1.6*x = 3.67*3.67
1.6*x = 13.4689
1.6*x/1.6 = 13.4689/1.6
x = 8.4180625

So BD is 8.4180625 meters
Use this to find the length of AD
AD = AB + BD
AD = 1.6 + 8.4180625
AD = 10.0180625
which rounds to 10.0 meters when rounding to the nearest tenth (one decimal place)

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Answer: choice D) 10.0 m

7 0

3 years ago

Hannah got a perfect score on 3 more spelling quizzes this quarter than last quarter . If she doubles the number of perfect quiz

algol13

First, underline the key numbers

n=Perfect Quizzes last quarter

x=School record

n+3

3•2=x

Now we solve that

3•2=6

Now we know, x=6

If the record (6) is 3 times the number of spelling quizzes Hannah scored perfectly last quarter (n), then we know we have to divide the record (6) by 3 to know how many perfect quizzes were from last quarter.

6/3=2 so, n=2

The number of perfectly scored quizzes from last quarter is 2.

7 0

3 years ago

Essay about how we use math in our every day life. Give me a paragraph or something pleaseee

AnnyKZ [126]

Answer:

Math is required in every day life. When you go to the grocery store determining which is the better deal. Or when cooking to figure out exactly what ingredients you need or hu=ow much. Math is required everyday to do very simple tasks

Step-by-step explanation:

3 0

1 year ago