# Substitution

Our substitution feature allows you to answer the question "What would be the value of this expression if we substituted a different value for A?," without ever changing the original value of A.

Using the ‘with’ substitution function, you can replace a variable in an expression with a constant value, another variable expression, or a list.

You can find this function in the “Advanced” section of the “Functions” menu on the keypad, or ‘with’ can also be typed directly into an expression line using your keyboard.

### Substitution within a Function

Where would the parabola $$f\left(x\right)=ax^{2}+bx+c$$ move if $$b$$ were $$-1$$? Model $$f\left(x\right)$$ after substituting $$b$$ with $$-1$$ to visualize the change. Next, trying graphing the vertex of the original function $$(V)$$ and using substitution to also graph the vertex when $$b = -1$$. ### Substitution within the Same Expression Line

You can evaluate expressions by substituting variables with constant values in the same line. You can also substitute a variable with another expression, but if that expression depends on a free variable, it will need to be defined separately. 