Formula for Finding Slope of a Straight Line

Q. What is the slope of the line shown in the image below?

Q. What is the slope of this horizontal straight line?

Q.

Using the concept of slope, prove that the points (a, b +c), (b, c+a) and (c, a+b) are in a straight line.

Q. Draw a 'more than' given for the data given below which gives the marks of $100$ students.

Marks	$0-10$	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$
Number of students	$4$	$6$	$10$	$10$	$25$	$22$	$18$	$5$

Q. What is the slope of the line joining the points $(x_1,y_1)$ and $(x_2,y_2)$?

1. $\frac{y_1}{x_2-x_1}$
2. $\frac{y_2}{x_2}$
3. $\frac{y_2-y_1}{x_2-x_1}$
4. $\frac{y_2}{x_1-x_2}$