To find the perimeter of a triangle, you can use the formula:
\[ \text{Perimeter} = \text{Side}_1 + \text{Side}_2 + \text{Side}_3 \]
In this case, you have:
- Side 1 = 15
- Side 2 = 10
- Side 3 = \(x\) (the unknown side)
We know that the perimeter is 40, so we can write the equation:
\[ 15 + 10 + x = 40 \]
Now, simplify the equation:
\[ 25 + x = 40 \]
To isolate \(x\), subtract 25 from both sides:
\[ x = 40 - 25 \]
\[ x = 15 \]
So, the equation you are looking for is:
\[ 15 + 10 + x = 40 \]
And the third side \(x\) is equal to 15.
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