How do you solve the following system: #4x+y=-7, 8x-y=19 #?

2 Answers
Ratnaker Mehta
Jul 13, 2016

The Soln. #: x=1, y=-11#

Explanation:

From the First eqn., we get #:y=-7-4x........(i)#

Sub.ing this #y# in the second eqn., we get,

#8x-(-7-4x)=19#

#rArr 8x+7+4x=19#

#rArr 12x=19-7=12#

#rArr x=12/12=1#

Then, by #(i), y=-7-4=-11#

Hence the Soln. #: x=1, y=-11#

EZ as pi
Jul 13, 2016

#x = 1 " and " y = -11#

Explanation:

Each of these equations can easily be written with #y# as the subject.

#y = -4x -7 " and " y = 8x-19#

Because #y=y# we can equate the expressions.

#8x -19 = -4x -7#

#12x = 12#

#x = 1#

There are now two equations for finding the value of #y#. It is a good idea to substitute the #x# value into both, to check that our answers are correct.

#y = -4(1) -7 " and " y = 8(1)-19#

#y = -11 " "y = -11#

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