How do you solve #9x+5y=-21# and #-2x+y=11# using substitution?

1 Answer

Answer:

#x =-4#, #y=3#. Solve the second equation for #y# and put the answer in terms of #x# into the first equation.

Explanation:

# -2x + y = 11#.

When you are trying to find something that is lost always work backwards. PEMDAS backwards become PE SADM
(if you lose something in PE you are a sad member of humanity.
so the opposite of #-2x = + 2x#

Add #+ 2x# to both sides of the equation

#-2x + 2x + y = y + 2x#

#-2x +2x = 0#

leaving

#y = 2x + 11#

Now substitute #+2x +11# into the first equation for #y# giving

#9x + 5(+2x + 11) = -21#

Remember PE always comes first. Use the distributive property to multiply #5 xx (+2x)# and #5 xx 11#. This gives

#9x + 10 x + 55 = -21#

You are trying to find x which you somehow lost so you are a SAD M. Subtract #55# from both sides.

#+ 55 -55 = 0" "# and #" "-21 - 55 = -76#

leaving you with

#19 x = -76#

SA are gone so now you have to Divide. (D M) divide both sides by #19#.

#(19x)/19 = - 76/19#

#19/19 = 1" "# and #" "- 76/19 = -4#. so

#x = -4#

Substitute #-4# into the first equation

#y = 11 + 2(-4)#

#y= 11 + (-8)#

#y = 3#

If you remember that when you are trying to find something lost you are a SAD M and you won't be sad.