Solve the Equation: Triangle Symbol + 7 = 10

To determine the value of the triangle, we begin with the equation given:

$\triangle + 7 = 10$

We want to isolate $\triangle$. To do so, we subtract 7 from both sides of the equation:

$\triangle + 7 - 7 = 10 - 7$

This simplifies to:

$\triangle = 3$

Thus, the value of the triangle is $3$.