If we have an equation of the form:
[tex]y-y_1=m(x-x_1)[/tex]and we need to find the y-intercept form we have to make the multiplications in the equations.
[tex]\begin{gathered} y-y_1=m(x-x_1) \\ y-y_1=mx-mx_1 \\ y=mx-mx_1+y_1 \end{gathered}[/tex]Then we compare the last equation with the slope-intercept form:
[tex]y=mx+b[/tex]Therefore, the y-intercept of the line will we the number:
[tex]-mx_1+y_1[/tex]