document.write( "Question 521313: How would I solve y = 15 - 3x and 7y + 3x = 15 using the substitution method? I tried plugging the y = 15 - 3x for the y but I came up with a decimal answer and I don't think it's supposed to be a decimal? \n" ); document.write( "
Algebra.Com's Answer #346420 by mananth(16946)![]() ![]() You can put this solution on YOUR website! 3 x + 1 y = 15 .............1 \n" ); document.write( "7 y = 15 -3 x ---------2 \n" ); document.write( "/ 7 = \n" ); document.write( " y = 2.14 -0.43 x \n" ); document.write( "Substitute y in (1) \n" ); document.write( "3 x + 1 ( 2.14 -0.43 x ) = 15 \n" ); document.write( "3 x + 2.14 + -0.43 x = 15 \n" ); document.write( "3 x -0.43 x = 15 -2.14 \n" ); document.write( "2.57 x = 12.86 \n" ); document.write( "/ 2.57 \n" ); document.write( "x= 5 \n" ); document.write( "Plug the value of x in (1) \n" ); document.write( "3 x + 1 y = 15 \n" ); document.write( "3 * 5 + 1 y = 15 \n" ); document.write( "15 + 1 y = 15 \n" ); document.write( "1 y = 0 \n" ); document.write( "/ 1 \n" ); document.write( "y= 0 \n" ); document.write( "m.ananth@hotmail.ca \n" ); document.write( " \n" ); document.write( " |