document.write( "Question 344844: finding the difference quotient\r
\n" ); document.write( "\n" ); document.write( "f(x+h)-f(x)/h\r
\n" ); document.write( "\n" ); document.write( " g(x)=3sqrt of x
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\n" ); document.write( "I can set it up but i can't get the right answer\r
\n" ); document.write( "\n" ); document.write( "3 sqrt x+h - 3sqrt of x/ h\r
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Algebra.Com's Answer #246735 by jsmallt9(3758)\"\" \"About 
You can put this solution on YOUR website!
You are exactly correct so far:
\n" ); document.write( "\"%283sqrt%28x%2Bh%29+-+3sqrt%28x%29%29%2F+h\"
\n" ); document.write( "As h approaches 0, this is still of the 0/0 form so we need to do more. With experience you will learn that the next step is to multiply the numerator and denominator by \"%283sqrt%28+x%2Bh%29+%2B+3sqrt%28x%29%29\". (You will see why after you see how this simplifies things.)
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\n" ); document.write( "In the numerator we can take advantage of the \"%28a%2Bb%29%28a-b%29+=+a%5E2+-+b%5E2\" pattern. (We'll leave the denominator factored for reasons you will see shortly.)
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\n" ); document.write( "Simplifying the numerator:
\n" ); document.write( "\"%289%28x%2Bh%29+-+%289x%29%29%2F+%28%28h%29%283sqrt%28x%2Bh%29+%2B+3sqrt%28x%29%29%29\"
\n" ); document.write( "\"%289x+%2B+9h+-+9x%29%2F+%28%28h%29%283sqrt%28x%2Bh%29+%2B+3sqrt%28x%29%29%29\"
\n" ); document.write( "\"9h%2F%28%28h%29%283sqrt%28x%2Bh%29+%2B+3sqrt%28x%29%29%29\"
\n" ); document.write( "At this point we will reduce the fraction. (And we can see why we didn't bother multiplying out the denominator.) The h's cancel:
\n" ); document.write( "\"9cross%28h%29%2F%28cross%28h%29%283sqrt%28x%2Bh%29+%2B+3sqrt%28x%29%29%29\"
\n" ); document.write( "\"9%2F%283sqrt%28x%2Bh%29+%2B+3sqrt%28x%29%29\"
\n" ); document.write( "We can factor out a 3 in the denominator:
\n" ); document.write( "\"9%2F%283%28sqrt%28x%2Bh%29+%2B+sqrt%28x%29%29%29\"
\n" ); document.write( "And cancel a factor of 3:
\n" ); document.write( "\"3%2F%28sqrt%28x%2Bh%29+%2B+sqrt%28x%29%29\"
\n" ); document.write( "This is the difference quotient. (As h approaches 0, this fraction is not of the 0/0 form.)
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