To find the perimeter of the triangle with the given side lengths, we need to add the expressions representing each side:
- The first side length is \( 5m - 2n \) centimeters.
- The second side length is \( 7m + 10p \) centimeters.
- The third side length is \( 8p - 9n \) centimeters.
Now, we will calculate the perimeter by summing these three side lengths:
\[ \text{Perimeter} = (5m - 2n) + (7m + 10p) + (8p - 9n) \]
Now let's combine like terms:
-
Combine \( 5m \) and \( 7m \): \[ 5m + 7m = 12m \]
-
Combine \( 10p \) and \( 8p \): \[ 10p + 8p = 18p \]
-
Combine \( -2n \) and \( -9n \): \[ -2n - 9n = -11n \]
Putting it all together, we have:
\[ \text{Perimeter} = 12m + 18p - 11n \]
Thus, the expression that represents the perimeter, in centimeters, of the triangle is:
\[ \boxed{12m + 18p - 11n} \]