Question 1090080
Left side  = Right side
When there is an " = " sign, you are saying
that this must be true.
You just can't say something that is obviously
wrong, like {{{ 4 = 7 }}}
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The rule that must be followed is:
Whatever you do to the left side, you MUST
also do to the right side also
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{{{ 7x - 2*( x + 5 ) = 1 - 2*( 4 - 3x ) }}}
I want to get all the terms with {{{ x }}} in them 
on one side. First I'll get rid of the parenthses
{{{ 7x - 2x - 10 = 1 - 8 + 6x }}}
Subtract {{{ 6x }}} from both sides
{{{ 7x - 2x - 6x - 10 = 1 - 8 }}}
Combine terms on both sides
{{{ 7x - 8x - 10 = -7 }}}
Do the subtraction of {{{ x }}} terms on the left side
{{{ -x - 10 = -7 }}}
Add {{{ 10 }}} to both sides
{{{ -x = 3 }}}
Now multiply both sides by {{{ -1 }}}
{{{ x = -3 }}}
Hope this helps