DE + EF = 4x+2
DE = x+7
EF = 7
Substitute these in
x + 7 + 7 = 4x + 2
x + 14 = 4x + 2
subtract x from both sides
14 = 3x + 2
subtract 2 from both sides
3x = 12
divide both sides by 3
x = 4
substitute this in to find the length of DE
DE = x + 7
(4) + 7 = 11
the answer is 11
From figure we can see that:
DE=DF -EF
x+7 = 4x+2-7
combining like terms
x+7=4x-5
subtract x on the right side from 4x
7=(4x-x) -5
7=3x-5
add 5 on the left side
7+5=3x
12=3x
divide both sides by 3
x=4
DE=x+7 =4+7
DE=11
