Question 110064
Given:
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{{{(-6x^2+14x)-(-3x^2+5x)}}}
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Two rules apply to this problem:
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1) If parentheses are preceded by a plus (+) sign (or an assumed + sign because there is no 
sign) the parentheses can be removed without changing the signs of the terms they contain. And
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2) If parentheses are preceded by a minus (-) sign they can be removed (along with the minus sign)
by changing the original signs of all the terms inside that set of parentheses.
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So, In the given problem, the first set of parentheses has a presumed + sign. Therefore,
according to rule 1, the first set of parentheses can be removed without affecting the
signs of the terms inside.  This changes the problem to:
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{{{-6x^2+14x-(-3x^2+5x)}}}
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For the remaining set of parentheses, rule 2 applies because the parentheses are preceded by a
minus sign. Erase the minus sign and the parentheses and change the signs of the terms inside
the parentheses. When you do that you get:
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{{{-6x^2+14x+3x^2-5x)}}}
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Now you can combine like terms.  {{{-6x^2}}} and {{{+ 3x^2}}} combine to give {{{-3x^2}}} and
{{{14x}}} and {{{-5x}}} combine to {{{9x}}}. The final result of this problem is:
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{{{-3x^2 + 9x}}}
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Hope this helps you to understand the process of solving this problem.