Answer:
[tex]c=5a+2b+8[/tex].
Step-by-step explanation:
1. Create an expression.
Using the fact that the perimeter of a triangle is just the sum of the lengh of all its sides, then the expression "[tex]18a+6b+15[/tex]" is the result of adding up all the sides of this triangle. Then, if we have 2 of the 3 sides, the resulting side must measure the difference between the perimeter and the sum of the 2 given sides.This is how to write it:
[tex]18a+6b+15-((5a+7)+(8a+4b))=c[/tex]; c is the given name for the third side.
2. Simplify the expression.
[tex]c=18a+6b+15-(5a+7+8a+4b)\\ \\c=18a+6b+15-(13a+7+4b)\\ \\c=18a+6b+15-13a-7-4b\\ \\c=5a+2b+8[/tex]
3. Express the result.
[tex]c=5a+2b+8[/tex].
