How do you solve the system #4x-y=25# and #4x+5y=-29#?

2 Answers
Sep 16, 2016

use the elimination method to solve the simultaneous equations:
4x-y=25>eq no 1
4x+5y=-29>eq no 2
eq no 1-eq no 2
4x -y =25
(-4x-5y=29)the signs become opposite in the subtraction
0 -6y =54
-6y=54
y=54/-6
y=-9.

put the value of y=-9 into eq no 1.
(try to put the value in the equation with smaller values)
4x-(-9)=25
4x+9=25
4x=25-9
4x=16
x=16/4
x=4
S.S{4,-9}(remember that the value of the variable which comes first according to the alphabetic arrangement is always written first)

Sep 16, 2016

Answer:

#{x,y}={-9,4}#

Explanation:

Solve by elimination and substitution

#color(blue)(4x-y=25#

#color(blue)(4x+5y=-29#

We could see that, we can eliminate #4x# from both the equation

Subtract

#rarr(4x-y=25)-(4x+5y=-29)#

#rarr-6y=54#

#color(green)(rArry=54/-6=-9#

Substitute the value of #y# to the first equation

#rarr4x-(-9)=25#

#rarr4x+9=25#

#rarr4x=25-9#

#rarr4x=16#

#color(green)(rArrx=16/4=4#

#:.color(purple)({x,y}={-9,4}#