### Author Topic: math  (Read 1665 times)

#### RuiLoureiro

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##### Re: math
« Reply #15 on: September 29, 2018, 07:39:40 AM »
mab,
So x=3 is not <=> x^2= 9

#### mabdelouahab

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• Posts: 403
##### Re: math
« Reply #16 on: September 29, 2018, 08:04:08 AM »
RuiLoureiro
x=3 ⇔ x^2 = 9
but x^2 = 9 <≠> x=3  ; (x= 3 or x=-3)

#### RuiLoureiro

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##### Re: math
« Reply #17 on: September 29, 2018, 08:09:01 AM »
RuiLoureiro
x=3 ⇔ x^2 = 9
but x^2 = 9 <≠> x=3  ; (x= 3 or x=-3)
x=3 is not <=> x^2 = 9 ; (x= 3 or x=-3)
or
x=3 is not <=> x^2 = 3^2

#### mabdelouahab

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• Posts: 403
##### Re: math
« Reply #18 on: September 29, 2018, 08:49:03 AM »
x=3 <=> x^2 = 9 because  x=3  <=> x^2= x * x = 3 * 3 = 9
x^2 = 9 is not <=> x=3 because (x^2 = 9) is a function that accepts two solutions x= 3 or x=-3

#### RuiLoureiro

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• Posts: 819
##### Re: math
« Reply #19 on: September 29, 2018, 09:01:58 AM »
x=3 <=> x^2 = 9 because  x=3  <=> x^2= x * x = 3 * 3 = 9
x^2 = 9 is not <=> x=3 because (x^2 = 9) is a function that accepts two solutions x= 3 or x=-3
x^2 = 9 is <=> x^2 - 3^2 = 0 is <=> (x-3)*(x+3)=0 is <=> x-3=0 or x+3=0
is <=> x=3 or x=-3. This is the correct way.
So x=3 => x^2 = 3^2. The sol of the left is {3}; the sol of the right is {-3,3}. {3} is a subset of {-3,3}. So x=3 => x^2=9 ( not <=> ).

#### mabdelouahab

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• Posts: 403
##### Re: math
« Reply #20 on: September 29, 2018, 09:32:27 AM »
So x=3 => x^2 = 3^2. The sol of the left is {3}; the sol of the right is {-3,3}. {3} is a subset of {-3,3}. So x=3 => x^2=9 ( not <=> ).
In this case you start from a value (=3)  not a variable, when we start with the value we get to the result.

#### K_F

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##### Re: math
« Reply #21 on: September 29, 2018, 11:47:57 PM »
hi K_F
In the first line:
√(2 + √(3)) *√(2)* (√(3) - 1)=2
not:
√(2 * √(3)) *√(2)* (√(3) - 1)=2
:redface:
Hah.. Thought I had missed something.. hadn't put the time into finding it..  :t
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