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All three sides of an equilateral triangle have equal lengths.
It gives you these equations
2x - 7 = y + 5, (1)
x + y - 9 = y + 5. (2)
It is your system of 2 equations in 2 unknowns.
From equation (2),
x = 5 + 9 = 14.
Substitute it into equation (1), replacing there x by 14
2*14 - 7 = y + 5.
It implies
28 - 7 = y + 5
21 = y + 5
y = 21 - 5 = 16.
Now, calculate the length of one side, for example, the length of the side 2x-7
2x - 7 = 2*14 - 7 = 21.
Check that the other sides also have the length of 21
x + y - 9 = 14 + 16 - 9 = 21
y + 5 = 16 + 5 = 21.
ANSWER. The side length of this equilateral triangle is 21 units.
Solved.
