document.write( "Question 503170: how do i solve the system using the substitution method for these two equations?
\n" ); document.write( " $\"+-x-4y=+-3+\"$
\n" ); document.write( " $\"+2x%2By=15+\"$ \n" ); document.write( "

Algebra.Com's Answer #339102 by Maths68(1474) $\"\"$ $\"About$

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-x-4y= -3 ...........(1)
\n" ); document.write( "2x+y=15 .............(2)
\n" ); document.write( "Take (1)
\n" ); document.write( "-x-4y= -3
\n" ); document.write( "-x=4y-3
\n" ); document.write( "Multiply by (-1) both sides of above equation
\n" ); document.write( "x=-4y+3
\n" ); document.write( "substitute the value of x in (2)
\n" ); document.write( "2(-4y+3)+y=15
\n" ); document.write( "-8y+6+y=15
\n" ); document.write( "-7y=15-6
\n" ); document.write( "-7y=9
\n" ); document.write( "Divide by -7 both sides of the above equation
\n" ); document.write( "-7y/-7=9/-7
\n" ); document.write( "y=9/-7
\n" ); document.write( "Put the value of y in (1)
\n" ); document.write( "-x-4(9/-7)= -3
\n" ); document.write( "Multiply by -7 both sides of the equation
\n" ); document.write( "7x-36=21
\n" ); document.write( "7x=21+36
\n" ); document.write( "7x=57
\n" ); document.write( "x=57/7\r
\n" ); document.write( "\n" ); document.write( "Solution set (57/7, -9/7)\r
\n" ); document.write( "\n" ); document.write( "Check
\n" ); document.write( "Put the values of x and y in either of two equations (1) or (2)
\n" ); document.write( "-x-4y= -3
\n" ); document.write( "-57/7-4(-9/7)=-3
\n" ); document.write( "-57/7-4(-9/7)=-3
\n" ); document.write( " Multiply by 7 both sides
\n" ); document.write( "-57-(4)(-9)=-3 * 7
\n" ); document.write( "-57+36=-21
\n" ); document.write( "-21=-21\r
\n" ); document.write( "\n" ); document.write( "2x+y=15
\n" ); document.write( "2(57/7)+(-9/7)=15
\n" ); document.write( "Multiply by 7 both sides
\n" ); document.write( "2(57)-9=15*7
\n" ); document.write( "114-9=105
\n" ); document.write( "105=105 \n" ); document.write( "

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