If the length of three sides are x, x+2, and 2x-40. Then x=27.
Because the perimeter of the triangle is the sum of the length of sides of the triangle. (3 sides. Since it's a triangle). Therefore,
the perimeter of the traingle = Length of side 1 + Length of side 2 + Length of side 3.
The lengths given are 1) x, 2) x+2, 3) 2x-40.
Therefore.
Perimeter = x + x+2 + 2x-40.
And since perimeter is equal to 70cm.
70 = x + x+2 + 2x-40.
70 = x + x + 2x -40 + 2.
70= 4x - 38
70+38 = 4x
108=4x
108/4=x
x=27.
Therefore.
length 1, which was x, is equal to 27.
length 2, which was x+2, is equal to (27+2) = 29.
length 3, which was 2x-40, is equal to ((2×27)-40) = 14.