To find midpoint between points $ A(x_1,y_1, z_1) $ and $ B(x_2,y_2, z_2) $, we use formula:

$$ M = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2}, \frac{z_1 + z_2}{2} \right) $$

In this example we have:

$$ \begin{aligned} & A \left(\dfrac{ 3 }{ 4 },~\dfrac{ 3 }{ 4 },~-1\right) \implies x_1 = \frac{ 3 }{ 4 }, ~~ y_1 = \frac{ 3 }{ 4 } ~~ \text{and} ~~ z_1 = \frac{ 3 }{ 4 } \\[1 em] & B \left(-\dfrac{ 11 }{ 2 },~\dfrac{ 3 }{ 2 },~0\right) \implies x_2 = -\frac{ 11 }{ 2 }, ~~ y_2 = \frac{ 3 }{ 2 } ~~ \text{and} ~~ z_2 = 0 \end{aligned} $$

After substituting into above formula, we get:

$$ \begin{aligned} M & \left( \frac{ \frac{ 3 }{ 4 } + \left( -\frac{ 11 }{ 2 }\right) }{2}, \frac{ \frac{ 3 }{ 4 } + \frac{ 3 }{ 2 } }{2}, \frac{ -1 + 0 }{2} \right) \\[1 em] M & \left( \frac{ -\frac{ 19 }{ 4 } }{2}, \frac{ \frac{ 9 }{ 4 } }{2}, \frac{ -1 }{2} \right) \\[1 em] M & \left(-\dfrac{ 19 }{ 8 },~\dfrac{ 9 }{ 8 },~-\dfrac{ 1 }{ 2 }\right) \end{aligned} $$

Midpoint Calculator