the equation of a line in point-slope form is
y - b = m(x - a)
where m is the slope and (a, b) a point on the line
to calculate m use the gradient formula
m = ( y₂ - y₁ ) / (x₂ - x₁ )
with (x₁, y₁ ) = (- 9, 7 ) and (x₂, y₂ ) = (3, 3 )
m = [tex]\frac{3-7}{3+9}[/tex] = [tex]\frac{-4}{12}[/tex] = - [tex]\frac{1}{3}[/tex]
using (a, b) = (3, 3 ), then
y - 3 = - [tex]\frac{1}{3}[/tex](x - 3 )
or using (a, b ) = (- 9, 7 ), then
y - 7 = - [tex]\frac{1}{3}[/tex](x + 9 )
