How do solve the following linear system?: # 4x+21y=6 , x+y=-1 #?

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Answer 1 · 2016-05-12T02:53:37

#x=-27/17#
#y=10/17#

Given -

#4x+21y=6# ------------------ (1)
#x+y=-1# --------------------(2)

Solve the equation (2) for #y#

#y=-1-x#

Substitute #y=-1-x# in equation (1)

#4x+21(-1-x)=6#

Simplify

#4x-21-21x=6#
#-17x=6+21#
#x=-27/17#

Substitute #x=-27/17# in equation (1)

#-27/17+y=-1#
#y=-1+27/17=(-17+27)/17=10/17#
#y=10/17#