Solve the Triangle Symbol Equation: △-3=70

To solve the equation $\triangle - 3 = 70$, we will use basic algebra to isolate the value of $\triangle$.

We start by adding 3 to both sides of the equation to isolate $\triangle$:

$\triangle - 3 + 3 = 70 + 3$

Notice that $-3 + 3$ on the left side simplifies to 0, which leaves us with:

$\triangle = 70 + 3$

Now, perform the arithmetic on the right side:

$\triangle = 73$

Hence, the numerical value of the triangle is $73$.