I dont understand why the slope =-1 and why we find slope in linear equation.

Recall the equation for a line is y = mx + b, where b is a constant (your intercept with the y-axis). The slope is -1 because every time you increase your x value (or your horizontal position on the graph, your y value (the vertical axis) decreases (thus the negative sign) by the same amount.

m (your slope) can be found with the formula:

**m = (y2 – y1)/(x2 – x1)**

Plugging in:

**m = (2 - 10)/(8 - 0) = - 1**

Keep in mind any two points on the line will work for this, not just those shown.

Or to put in terms of this graph, every time you gain an apple, you loose a banana, and vice versa.

Also, this may seem very basic/simple, but as you will see later in neural networks, at least with regards to forward propagation, this is basically what the network is calculating-- Just on steroids (with a few other tricks thrown in). It will surprise you. I know it surprised me.

@itsShayanProfile Can you show me what numbers you are using for the formula I gave you ?

Note: You have two unknowns here so you have to look at the points on the line-- Otherwise it is unsolvable given only on equation.