Remark
All three sides are equal in an equilateral triangle.
y + 5 = x + y - 5 . . . . . . .(1)
y +5 = 2x - 7 . . . . . . . . .(2)
For 1
Subtract y from both sides.
5 = x - 5 . . . . . . . . . . . Add 5 to both sides.
x = 10
x + y - 10 = 2x - 7 . . . .Put x = 10 into this equation
10 + y - 10 = 2*10 - 7
y = 20 - 7
y = 13
In 2x - 7, let x = 10
2(10) - 7 = 20 - 7
