How do you solve #2x + 7y = 30# and #x = 48 - 9y# using substitution?

1 Answer
EZ as pi
May 11, 2016

#y = 6#

Explanation:

#2x + 7y = 30 " " and " " color(red)(x = 48 - 9y) #

Remember that the = sign tells us that two expressions are absolutely the same as each other - specifically that they are inter-changeable! In these equations: #"x IS THE SAME AS (48 - 9y)"#.

So, in the first equation an #x# can be replaced by (48 - 9y).

#2color(red)x + 7y = 30 " " rArr 2color(red)((48 - 9y)) + 7y = 30#

#2(48 - 9y) + 7y = 30#
#96 - 18y + 7y = 30#
#96 - 30 = 18y - 7y#

#66 = 11y#

#6 = y#

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