How do you solve this system of equations by substitution: # - x+y = 40 and y = 9x#?

2 Answers
Pallu
Dec 10, 2017

#x=5 and y= 45#

Explanation:

#- x+y = 40# ----- let this be equation (1)and
# y = 9x# ------be equation (2)

Substitute value of #y# from equation(2) in equation(1):

(1) #=> -x + (9x) = 40#

#=> 8x = 40#

#=> x=40/8 =5#

Now substitute this value of #x# in equation(2) :

#=> y= 9x =9xx5 =45#

#therefore x=5 and y= 45#

Jim G.
Dec 10, 2017

#x,y)to(5,45)#

Explanation:

#-x+y=40to(1)#

#y=9xto(2)#

#color(blue)"substitute "y=9x" into equation "(1)#

#-x+9x=40#

#rArr8x=40#

#"divide both sides by 8"#

#(cancel(8) x)/cancel(8)=40/8#

#rArrx=5#

#"substitute this value into equation "(2)#

#y=9xx5=45#

#rArr"point of intersection "=(5,45)#

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