An equation of a line in point-slope form: y - y₁ = m(x - x₁)
1.
passes through (1, 9) ⇒ x₁ = 1, y₁ = 9
slope: m = 2
The equation:
y - 9 = 2(x - 1) ← point-slope form
y - 9 = 2x - 2 {add 9 to both sides}
y = 2x + 7 ← slope-intercept form
2.
passes through (4, -1) ⇒ x₁ = 4, y₁ = -1
slope: m = -3
The equation:
y + 1 = -3(x - 4) ← point-slope form
y + 1 = -3x + 12 {subtract 1 from both sides}
y = -3x + 11 ← slope-intercept form
