document.write( "Question 470687: The function f is defined by f(x)=x^3 - 4x. The function of g is defined by g(x)=f(x+h)+k where h and k are constants. What is the value of hk?\r
\n" ); document.write( "\n" ); document.write( "Points for y=f(x)are (-1,3), (1,-3)
\n" ); document.write( "Points for y=g(x) are (2,1), (4,-5)\r
\n" ); document.write( "\n" ); document.write( "The answer is 6, but I do not understand how they came up with this answer. Please help!
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Algebra.Com's Answer #322857 by MathLover1(20850)\"\" \"About 
You can put this solution on YOUR website!
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\n" ); document.write( "\n" ); document.write( "First \"y+=+f%28x%29+\"and \"f%28x%29+=+x%5E3+-+4x\", \"y+=+g%28x%29+\"and \"g%28x%29+=+f%28x+%2B+h%29+%2B+k\" or \r
\n" ); document.write( "\n" ); document.write( "\"y+=+f%28x%29+=+x%5E3+-4x\"
\n" ); document.write( "\"y+=+g%28x%29+=+f%28x+%2B+h%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "Looks to me like we have two equations for \"y\" which means we can solve them as a system. Notice that \"g%28x%29+\"contains \"f%28x%29\" but with a different input variable, namely \"%28x+%2B+h%29\". \r
\n" ); document.write( "\n" ); document.write( "To find \"f%28x+%2B+h%29\" we replace\"+x\" with \"%28x+%2B+h%29\" wherever we find an \"x\" in the \"f\" equation.\r
\n" ); document.write( "\n" ); document.write( "\"f%28x%29+=+x%5E3+-+4x\" will become\r
\n" ); document.write( "\n" ); document.write( "\"f%28x+%2B+h%29+=+%28x+%2B+h%29%5E3+-+4%28x+%2B+h%29\"\r
\n" ); document.write( "\n" ); document.write( "So now we replace \"f%28x+%2B+h%29\" in \"g%28x%29\" with our new result.\r
\n" ); document.write( "\n" ); document.write( "\"g%28x%29+=+f%28x+%2B+h%29+%2Bk\"\r
\n" ); document.write( "\n" ); document.write( "\"g%28x%29+=+%28+%28x+%2B+h%29%5E3+-+4%28x+%2B+h%29+%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "Also, we are given a pair of points that work with \"g%28x%29\" so lets plot them in and get a pair of equations. The first number in each point is \"x+\"and the second is \"y\".\r
\n" ); document.write( "\n" ); document.write( "Points in g(x) : (\"2\", \"1\") and (\"4\", \"-5\")\r
\n" ); document.write( "\n" ); document.write( "So for the first :\r
\n" ); document.write( "\n" ); document.write( "\"1+=+%282+%2B+h%29%5E3+-+4%282+%2B+h%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=+%288+%2B+12h+%2B+6h%5E2+%2B+h%5E3%29+-+%288+%2B+4h%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=+8+%2B+12h+%2B+6h%5E2+%2B+h%5E3+-+8+-+4h+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=+h%5E3+%2B+6h%5E2+%2B+8h+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+-+%28h%5E3+%2B+6h%5E2+%2B+8h%29+=+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-+h%5E3+-+6h%5E2+-+8h+%2B+1+=+k\"\r
\n" ); document.write( "\n" ); document.write( "and for the second :\r
\n" ); document.write( "\n" ); document.write( "\"-5+=+%284+%2B+h%29%5E3+-+4%284+%2B+h%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-5+=+%2864+%2B+48h+%2B+12h%5E2+%2B+h%5E3%29+-+%2816+%2B+4h%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-5+=+64+%2B+48h+%2B+12h%5E2+%2B+h%5E3+-+16+-+4h+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-5+=+h%5E3+%2B+12h%5E2+%2B+44h+%2B+48+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-5+-+%28h%5E3+%2B+12h%5E2+%2B+44h+%2B+48%29+=+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-+h%5E3+-+12h%5E2+-+44h+-+53+=+k\"\r
\n" ); document.write( "\n" ); document.write( "Notice that both long equations are equal to \"k\". That means they are also equal to each other.\r
\n" ); document.write( "\n" ); document.write( "\"-+h%5E3+-+6h%5E2+-+8h+%2B+1+=+-+h%5E3+-+12h%5E2+-+44h+-+53\"\r
\n" ); document.write( "\n" ); document.write( "\"-+h%5E3+-+6h%5E2+-+8h+%2B+1+-+%28-+h%5E3+-+12h%5E2+-+44h+-+53%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"-+h%5E3+-+6h%5E2+-+8h+%2B+1+%2B+h%5E3+%2B+12h%5E2+%2B+44h+%2B+53+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"6h%5E2+%2B+36h+%2B+54+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"6%28h%5E2+%2B+6h+%2B+9%29+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"%28h+%2B+3%29%28h+%2B+3%29+=+0+%2F+6\"\r
\n" ); document.write( "\n" ); document.write( "\"h+%2B+3+=+0\"\r
\n" ); document.write( "\n" ); document.write( "\"h+=+-3\"\r
\n" ); document.write( "\n" ); document.write( "So\"+h\" is \"-3\", now we need \"k\".\r
\n" ); document.write( "\n" ); document.write( "\"g%28x%29+=+%28+%28x+%2B+h%29%5E3+-+4%28x+%2B+h%29+%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"y+=+%28+%28x+%2B+h%29%5E3+-+4%28x+%2B+h%29+%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=%28+%282+-+3%29%5E3+-+4%282+-+3%29%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=+-1%5E3+-+4%28-1%29+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=+-1+%2B+4+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"1+=+3+%2B+k\"\r
\n" ); document.write( "\n" ); document.write( "\"-2+=+k\"\r
\n" ); document.write( "\n" ); document.write( "So \"k+\"is \"-2\". We already know that \"h\" is \"-3\". so :\r
\n" ); document.write( "\n" ); document.write( "\"hk+=+-3%2A-2=6\"\r
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