document.write( "Question 1172668: The force of attraction (F) between two opposite electric charges varies inversely as the square of the distance (d) between them. If F = 30 newtons when d = 5 meters, find F when d = 12 meters.
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Algebra.Com's Answer #797784 by Edwin McCravy(20060)\"\" \"About 
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The force of attraction (F) between two opposite electric charges varies inversely as the square of the distance (d) between them.
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document.write( "Let's pause here.\r\n" );
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document.write( "For all proportion problems, start with this:\r\n" );
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document.write( "Varying           \"directly\" or product of \"jointlys\" or 1 if none \r\n" );
document.write( "quantity  = k ∙ ----------------------------------------------------------\r\n" );
document.write( "                inversely variable or product of \"inverselys\" or 1 if none\r\n" );
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document.write( "In this problem the varying quantity is F. There are no \"directly\" or \"jointly\"\r\n" );
document.write( "variable.  So the numerator is the number 1.  We have one inversely, d2. So we\r\n" );
document.write( "have F on the left, 1 on the top of the fraction and d2 on the bottom:\r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2Ck%2Aexpr%281%5E%22%22%2Fd%5E2%29%29\"\r\n" );
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If F = 30 newtons when d = 5 meters,
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document.write( "Let's pause again here.\r\n" );
document.write( "Let's substitute 30 for F in \"matrix%281%2C3%2CF%2C%22%22=%22%22%2Ck%2Aexpr%281%5E%22%22%2Fd%5E2%29%29\", and 5 for d2>/sub>, and solve for k:\r\n" );
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document.write( "\"matrix%281%2C3%2C30%2C%22%22=%22%22%2Ck%2Aexpr%281%5E%22%22%2F5%5E2%29%29\"\r\n" );
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document.write( "Put 1 under 30 and write 52 as 25:\r\n" );
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document.write( "\"matrix%281%2C3%2C30%2F1%2C%22%22=%22%22%2Ck%2F25%29\"\r\n" );
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document.write( "Cross-multiply:\r\n" );
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document.write( "\"matrix%281%2C3%2Ck%2C%22%22=%22%22%2C750%29\"\r\n" );
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document.write( "Now we substitute 750 for k in \r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2Ck%2Aexpr%281%5E%22%22%2Fd%5E2%29%29\"\r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2C750%2Aexpr%281%5E%22%22%2Fd%5E2%29%29\"\r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2C750%5E%22%22%2Fd%5E2%29\"\r\n" );
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document.write( " find F when d = 12 meters.\r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2C750%5E%22%22%2F12%5E2%29\"\r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2C750%2F144%29\"\r\n" );
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document.write( "\"matrix%281%2C3%2CF%2C%22%22=%22%22%2C5.208333333%29\" newtons.\r\n" );
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document.write( "Edwin
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