document.write( "Question 87678: I really need help on this problem: If f is a linear function and f(0)= 10 and
\n" ); document.write( "f(10)= 14, find f(5) and f(-5).
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Algebra.Com's Answer #63582 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
If \"f%280%29=10\" this means we have a point (0,10). If \"f%2810%29=14\" this means we have a point (10,14). So we can find the equation of the line through the two points\r
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Solved by pluggable solver: Finding the Equation of a Line
First lets find the slope through the points (\"0\",\"10\") and (\"10\",\"14\")
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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 (\"0\",\"10\") and (\"x%5B2%5D\",\"y%5B2%5D\") is the second point (\"10\",\"14\"))
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\n" ); document.write( " \"m=%2814-10%29%2F%2810-0%29\" Plug in \"y%5B2%5D=14\",\"y%5B1%5D=10\",\"x%5B2%5D=10\",\"x%5B1%5D=0\" (these are the coordinates of given points)
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\n" ); document.write( " \"m=+4%2F10\" Subtract the terms in the numerator \"14-10\" to get \"4\". Subtract the terms in the denominator \"10-0\" to get \"10\"
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\n" ); document.write( " \"m=2%2F5\" Reduce
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\n" ); document.write( " So the slope is
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\n" ); document.write( " \"m=2%2F5\"
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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-10=%282%2F5%29%28x-0%29\" Plug in \"m=2%2F5\", \"x%5B1%5D=0\", and \"y%5B1%5D=10\" (these values are given)
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\n" ); document.write( " \"y-10=%282%2F5%29x%2B%282%2F5%29%280%29\" Distribute \"2%2F5\"
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\n" ); document.write( " \"y-10=%282%2F5%29x%2B0\" Multiply \"2%2F5\" and \"0\" to get \"0%2F5\". Now reduce \"0%2F5\" to get \"0\"
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\n" ); document.write( " \"y=%282%2F5%29x%2B0%2B10\" Add \"10\" to both sides to isolate y
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\n" ); document.write( " \"y=%282%2F5%29x%2B10\" Combine like terms \"0\" and \"10\" to get \"10\"
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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 (\"0\",\"10\") and (\"10\",\"14\") is:\"y=%282%2F5%29x%2B10\"
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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=2%2F5\" and the y-intercept is \"b=10\"
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\n" ); document.write( " Notice if we graph the equation \"y=%282%2F5%29x%2B10\" and plot the points (\"0\",\"10\") and (\"10\",\"14\"), we get this: (note: if you need help with graphing, check out this solver)
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\n" ); document.write( " Graph of \"y=%282%2F5%29x%2B10\" through the points (\"0\",\"10\") and (\"10\",\"14\")
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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 now we have the equation\r
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\n" ); document.write( "\n" ); document.write( "\"y=%282%2F5%29x%2B10\"\r
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\n" ); document.write( "\n" ); document.write( "which means \"f%28x%29=%282%2F5%29x%2B10\"\r
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\n" ); document.write( "\n" ); document.write( "Lets now find \"f%285%29\" \r
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\n" ); document.write( "\n" ); document.write( "\"f%285%29=%282%2F5%29%285%29%2B10\" Plug in \"x=5\"\r
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\n" ); document.write( "\n" ); document.write( "\"f%285%29=%2810%2F5%29%2B10\" Multiply\r
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\n" ); document.write( "\n" ); document.write( "\"f%285%29=2%2B10\" Reduce\r
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\n" ); document.write( "\n" ); document.write( "\"f%285%29=12\" Add\r
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\n" ); document.write( "\n" ); document.write( "So \"f%285%29=12\"\r
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\n" ); document.write( "\n" ); document.write( "Lets now find \"f%28-5%29\" \r
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\n" ); document.write( "\n" ); document.write( "\"f%28-5%29=%282%2F5%29%28-5%29%2B10\" Plug in \"x=-5\"\r
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\n" ); document.write( "\n" ); document.write( "\"f%28-5%29=%28-10%2F5%29%2B10\" Multiply\r
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\n" ); document.write( "\n" ); document.write( "\"f%28-5%29=-2%2B10\" Reduce\r
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\n" ); document.write( "\n" ); document.write( "\"f%28-5%29=8\" Add\r
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\n" ); document.write( "\n" ); document.write( "So \"f%28-5%29=8\"\r
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\n" ); document.write( "\n" ); document.write( "Notice if we graph \"y=%282%2F5%29x%2B10\" we get:\r
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\n" ); document.write( "\n" ); document.write( "graph of \"y=%282%2F5%29x%2B10\" which goes through the points (0,10),(10,14),(5,12),(-5,8)\r
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\n" ); document.write( "\n" ); document.write( "Notice how the line goes through all of the points. This verifies our answer.
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