To calculate the straight-line distance between two points in a triangle, we need to clarify a few things:

• Are $A$ and $B$ representing the lengths of two sides of the triangle?
• Or are $A$ and $B$ the coordinates of points?

For now, I'll assume that $A$ and $B$ are side lengths of a right-angled triangle, and you want to find the hypotenuse (straight-line distance between the two other points) using the Pythagorean theorem:

$c = \sqrt{A^2 + B^2}$

Where $A = \frac{3}{10}$ and $B = \frac{3}{5}$.

Let’s calculate it:

1. Square the values of $A$ and $B$: $A^2 = \left(\frac{3}{10}\right)^2 = \frac{9}{100}$ $B^2 = \left(\frac{3}{5}\right)^2 = \frac{9}{25}$

2. Add the squared values: $A^2 + B^2 = \frac{9}{100} + \frac{9}{25} = \frac{9}{100} + \frac{36}{100} = \frac{45}{100} = \frac{9}{20}$

3. Take the square root to find $c$: $c = \sqrt{\frac{9}{20}} = \frac{3}{\sqrt{20}} = \frac{3}{2\sqrt{5}} \approx 0.6708$

Thus, the straight-line distance $c$ is approximately 0.6708.

Would you like more details on this, or do you have any questions?

Related Questions:

1. What is the distance formula in coordinate geometry?
2. How does the Pythagorean theorem apply to non-right triangles?
3. What are other methods to calculate distances in triangles?
4. How can trigonometry help in calculating side lengths of a triangle?
5. Can this approach be extended to 3D space?

Tip: Always make sure you know the type of triangle you're dealing with before applying a specific method!