document.write( "Question 252213: Hi! how do you do substitution method for: 9x+5y=-6
\n" ); document.write( " 4x+3y=2
\n" ); document.write( "

Algebra.Com's Answer #184044 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Start with the given system of equations:\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"system%289x%2B5y=-6%2C4x%2B3y=2%29\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Now in order to solve this system by using substitution, we need to solve (or isolate) one variable. I'm going to solve for y.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So let's isolate y in the first equation\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"9x%2B5y=-6\" Start with the first equation\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"5y=-6-9x\" Subtract \"9x\" from both sides\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"5y=-9x-6\" Rearrange the equation\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=%28-9x-6%29%2F%285%29\" Divide both sides by \"5\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=%28%28-9%29%2F%285%29%29x%2B%28-6%29%2F%285%29\" Break up the fraction\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=%28-9%2F5%29x-6%2F5\" Reduce\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "---------------------\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Since \"y=%28-9%2F5%29x-6%2F5\", we can now replace each \"y\" in the second equation with \"%28-9%2F5%29x-6%2F5\" to solve for \"x\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"4x%2B3highlight%28%28%28-9%2F5%29x-6%2F5%29%29=2\" Plug in \"y=%28-9%2F5%29x-6%2F5\" into the second equation. In other words, replace each \"y\" with \"%28-9%2F5%29x-6%2F5\". Notice we've eliminated the \"y\" variables. So we now have a simple equation with one unknown.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"4x%2B%283%29%28-9%2F5%29x%2B%283%29%28-6%2F5%29=2\" Distribute \"3\" to \"%28-9%2F5%29x-6%2F5\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"4x-%2827%2F5%29x-18%2F5=2\" Multiply\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"%285%29%284x-%2827%2F5%29x-18%2F5%29=%285%29%282%29\" Multiply both sides by the LCM of 5. This will eliminate the fractions (note: if you need help with finding the LCM, check out this solver)\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"20x-27x-18=10\" Distribute and multiply the LCM to each side\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"-7x-18=10\" Combine like terms on the left side\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"-7x=10%2B18\"Add 18 to both sides\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"-7x=28\" Combine like terms on the right side\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x=%2828%29%2F%28-7%29\" Divide both sides by -7 to isolate x\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x=-4\" Divide\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "-----------------First Answer------------------------------\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So the first part of our answer is: \"x=-4\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Since we know that \"x=-4\" we can plug it into the equation \"y=%28-9%2F5%29x-6%2F5\" (remember we previously solved for \"y\" in the first equation).\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=%28-9%2F5%29x-6%2F5\" Start with the equation where \"y\" was previously isolated.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=%28-9%2F5%29%28-4%29-6%2F5\" Plug in \"x=-4\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=36%2F5-6%2F5\" Multiply\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"y=6\" Combine like terms and reduce. (note: if you need help with fractions, check out this solver)\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "-----------------Second Answer------------------------------\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So the second part of our answer is: \"y=6\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "-----------------Summary------------------------------\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So our answers are:\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x=-4\" and \"y=6\"\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "which form the point \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Now let's graph the two equations (if you need help with graphing, check out this solver)\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "From the graph, we can see that the two equations intersect at . This visually verifies our answer.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " graph of \"9x%2B5y=-6\" (red) and \"4x%2B3y=2\" (green) and the intersection of the lines (blue circle).\r
\n" ); document.write( "\n" ); document.write( "
\n" ); document.write( "
\n" );