Question 89080
Given:
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{{{10*sqrt(3) - 7*sqrt(3) + 5*sqrt(3)}}}
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To combine these terms just combine the multipliers of {{{sqrt(3)}}} and multiply the 
result of this combination by {{{sqrt(3)}}} to give you {{{8*sqrt(3)}}}.
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Another way of looking at the problem is that since every one of the terms has {{{sqrt(3)}}}
as a factor it can be factored out. The result is:
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{{{sqrt(3)*(10 - 7 + 5)}}}
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Then combine the terms inside the parentheses. 10 - 7 + 5 = +8. So you can replace the three
terms in the parentheses by +8 and the problem becomes:
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{{{sqrt(3)*(8)}}}
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and by convention we normally write this in the reverse order: {{{8*sqrt(3)}}}.
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Therefore, the third answer in your list of answers is the correct one ...
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Hope this helps you to understand the problem.