Solution:
An Isosceles triangle has two out of three of its sides to be equal.
Thus, we have
Given that the perimeter of the triangle is 7.5 m, this implies that
[tex]x+x+y=7.5[/tex]The shortest side of the triangle is y.
This implies that
[tex]y=2.1\text{ m}[/tex]By substitution, we have
[tex]\begin{gathered} x+x+2.1=7.5 \\ \Rightarrow2x+2.1=7.5 \end{gathered}[/tex]Hence, the equation that can be used to find the value of x is
[tex]2x+2.1=7.5[/tex]The correct option is D
