Write an equation of a line given its slope and y-intercept
we found the slope of a line from the equation of the line by solving the equation for y. For example, we found that the slope of the line with equation
y = 4x + 8
is 4, the coefficient of x. What does the number 8 represent?
To find out, suppose a line has slope m and y-intercept (0, b). We can find an equation of this line by choosing another point (x, y) on the line, as shown in Figure . Using the slope formula,
m = 
m = 
mx = y – b Milyiply byx.
mx + b = y Add b.
y = mx + b.
This last equation is called the slope-intercept form of the equation of a line, because we can identify the slope m and y-intercept (0, b) at a glance.