**Finding the Equivalent Resistance in a Square Configuration of Resistors**

To determine the equivalent resistance between two diagonally opposite points in a square configuration of resistors, we can follow these steps:

**Step 1: Understanding the Problem**

We are given a square configuration of resistors, where each resistor has a resistance of 4 ohms. Our goal is to find the equivalent resistance between two diagonally opposite points in the square.

**Step 2: Identifying the Configuration**

The given configuration of resistors forms a square, with each resistor connected to its adjacent resistors. This arrangement creates a network of resistors.

**Step 3: Analyzing the Configuration**

To simplify the analysis, we can start by labeling the corners of the square as A, B, C, and D. Let's assume that we want to find the equivalent resistance between points A and C, which are diagonally opposite.

**Step 4: Redrawing the Configuration**

To better understand the configuration, we can redraw it in a more systematic manner. We can represent the resistors as a grid, with each resistor labeled with its resistance value.

```
A ----- 4Ω ----- B
| |
4Ω 4Ω
| |
C ----- 4Ω ----- D
```

**Step 5: Simplifying the Configuration**

To find the equivalent resistance between points A and C, we can simplify the configuration by combining resistors. We can observe that resistors AB and CD are connected in parallel, while resistors AC and BD are connected in series.

**Step 6: Calculating the Equivalent Resistance**

To find the equivalent resistance of resistors AB and CD, we can use the formula for resistors in parallel:

```
1/Req = 1/R1 + 1/R2 + ...
```

```
1/Req_AB_CD = 1/4Ω + 1/4Ω
= 2/4Ω
= 1/2Ω
```

Therefore, the equivalent resistance of resistors AB and CD is 1/2Ω.

**Step 7: Calculating the Equivalent Resistance**

To find the equivalent resistance of resistors AC and BD, we can use the formula for resistors in series:

```
Req = R1 + R2 + ...
```

```
Req_AC_BD = 4Ω + 4Ω
= 8Ω
```

Therefore, the equivalent resistance of resistors AC and BD is 8Ω.

**Step 8: Calculating the Equivalent Resistance**

Finally, to find the equivalent resistance between points A and C, we need to calculate the total resistance when resistors AB and CD are connected in parallel with resistors AC and BD connected in series.

```
Req_total = Req_AB_CD + Req_AC_BD
= 1/2Ω + 8Ω
= 8.5Ω
```

Therefore, the equivalent resistance between points A and C in the square configuration of resistors is 8.5 ohms.

In conclusion, by understanding the given configuration and applying the principles of resistors in parallel and series, we can determine the equivalent resistance between two diagonally opposite points in a square configuration of resistors.