document.write( "Question 76164This question is from textbook Algebra 1
\n" ); document.write( ": What is the equation for the line passing through the points (7,-8) and (-4, -4)? \n" ); document.write( "
Algebra.Com's Answer #54699 by jim_thompson5910(35256)\"\" \"About 
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Solved by pluggable solver: Finding the Equation of a Line
First lets find the slope through the points (\"7\",\"-8\") and (\"-4\",\"-4\")
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\n" ); document.write( " \"m=%28y%5B2%5D-y%5B1%5D%29%2F%28x%5B2%5D-x%5B1%5D%29\" Start with the slope formula (note: (\"x%5B1%5D\",\"y%5B1%5D\") is the first point (\"7\",\"-8\") and (\"x%5B2%5D\",\"y%5B2%5D\") is the second point (\"-4\",\"-4\"))
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\n" ); document.write( " \"m=%28-4--8%29%2F%28-4-7%29\" Plug in \"y%5B2%5D=-4\",\"y%5B1%5D=-8\",\"x%5B2%5D=-4\",\"x%5B1%5D=7\" (these are the coordinates of given points)
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\n" ); document.write( " \"m=+4%2F-11\" Subtract the terms in the numerator \"-4--8\" to get \"4\". Subtract the terms in the denominator \"-4-7\" to get \"-11\"
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\n" ); document.write( " \"m=-4%2F11\" Reduce
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\n" ); document.write( " So the slope is
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\n" ); document.write( " \"m=-4%2F11\"
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\n" ); document.write( "Now let's use the point-slope formula to find the equation of the line:
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\n" ); document.write( " ------Point-Slope Formula------
\n" ); document.write( " \"y-y%5B1%5D=m%28x-x%5B1%5D%29\" where \"m\" is the slope, and (\"x%5B1%5D\",\"y%5B1%5D\") is one of the given points
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\n" ); document.write( " So lets use the Point-Slope Formula to find the equation of the line
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\n" ); document.write( " \"y--8=%28-4%2F11%29%28x-7%29\" Plug in \"m=-4%2F11\", \"x%5B1%5D=7\", and \"y%5B1%5D=-8\" (these values are given)
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\n" ); document.write( " \"y%2B8=%28-4%2F11%29%28x-7%29\" Rewrite \"y--8\" as \"y%2B8\"
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\n" ); document.write( " \"y%2B8=%28-4%2F11%29x%2B%28-4%2F11%29%28-7%29\" Distribute \"-4%2F11\"
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\n" ); document.write( " \"y%2B8=%28-4%2F11%29x%2B28%2F11\" Multiply \"-4%2F11\" and \"-7\" to get \"28%2F11\"
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\n" ); document.write( " \"y=%28-4%2F11%29x%2B28%2F11-8\" Subtract \"8\" from both sides to isolate y
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\n" ); document.write( " \"y=%28-4%2F11%29x-60%2F11\" Combine like terms \"28%2F11\" and \"-8\" to get \"-60%2F11\" (note: if you need help with combining fractions, check out this solver)
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\n" ); document.write( " Answer:
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\n" ); document.write( " So the equation of the line which goes through the points (\"7\",\"-8\") and (\"-4\",\"-4\") is:\"y=%28-4%2F11%29x-60%2F11\"
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\n" ); document.write( " The equation is now in \"y=mx%2Bb\" form (which is slope-intercept form) where the slope is \"m=-4%2F11\" and the y-intercept is \"b=-60%2F11\"
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\n" ); document.write( " Notice if we graph the equation \"y=%28-4%2F11%29x-60%2F11\" and plot the points (\"7\",\"-8\") and (\"-4\",\"-4\"), we get this: (note: if you need help with graphing, check out this solver)
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\n" ); document.write( " Graph of \"y=%28-4%2F11%29x-60%2F11\" through the points (\"7\",\"-8\") and (\"-4\",\"-4\")
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\n" ); document.write( " Notice how the two points lie on the line. This graphically verifies our answer.
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\n" ); document.write( "\n" ); document.write( "So in other words, the equation is:\r
\n" ); document.write( "\n" ); document.write( "\"y=%28-4%2F11%29x-60%2F11\"
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