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3 years ago

I think of a number double it add 15 my number is 21 what number was i thinking about

Mathematics

1 answer:

AleksandrR [38]3 years ago

5 0

Hello from MrBillDoesMath!

Answer:

Discussion:

Let the number be "n",

2n + 15 = 21 => subtract 15 from both sides

2n = 21 - 15 = 6 => divide both sides by 2

n = 6/2 = 3

Check: Start with 3. Double it (gives 6), add 15 to it ( 6 + 15) which gives 21/

Thank you,

MrB

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saul85 [17]

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2 years ago

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3 years ago

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Marina86 [1]

Answer :

Let's assume the opposite of the statement i.e., 3 + √5 is a rational number.

$\\ \sf \: 3 + \sqrt{5} = \frac{a}{b} \\ \\ \qquad \: \tiny \sf{(where \: \: a \: \: and \: \: b \: \: are \: \: integers \: \: and \: \: b \: \neq \: 0)} \\$

$\\ \sf \: \sqrt{5} = \frac{a}{b} - 3 = \frac{a - 3b}{b} \\$

Since, a, b and 3 are integers. So,

$\\ \sf \: \frac{p - 3b}{b} \\ \\ \qquad \tiny \sf{ \: (is \: \: a \: \: rational \: \: number \:) } \\$

Here, it contradicts that √5 is an irrational number.

because of the wrong assumption that 3 + √5 is a rational number.

$\\$

Hence, 3 + √5 is an irrational number.

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