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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