The perimeter of an equilateral triangle is d cm. Write down an expression for the length, in centimeters, of each of the two sides.

Triangles have 3 sides!  An equilateral triangle has all sides equal, so their length is d/3 cm

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here is the answer \(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\begin{pmatrix} 1\\ 2 \end{pmatrix}\begin{bmatrix} 1 && 2 \\ 3 && 4 \end{bmatrix}\theta \Delta \Leftarrow\left ( \right )\begin{bmatrix} 1 && 2 \\ 3 && 4 \end{bmatrix}\varepsilon {}^{}\Delta \)

Let the third side=c, then we have:

d - c=Length of the two equilateral sides, and:

(d - c) / 2=Length of each of the equilateral sides.