How do you solve #x-5y=4# and #4x+8y=-5# using substitution?

1 Answer
Jim G.
Mar 11, 2016

#x = 1/4 , y = -3/4 #

Explanation:

Begin by labelling the equations- easier to follow.

x - 5y = 4 ................................(A)

4x + 8y = -5 ..............................(B)

Rearrange (A) to obtain : x = 4 + 5y ...................(C)

Now substitute this for x in (B)
4(4 + 5y ) + 8y = -5 → 16 + 20y+8y = -5 → # y = -21/28 = -3/4 #
now substitute # y = -3/4 " in " (C) #
# x = 4 + 5xx(-3/4) = 1/4 #
Check by substituting values of x and y in (A) and (B)

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