Persamaan garis yg melalui titik A(2,1) dan titik B(-2,-7) adalah

A (2,1)   ⇒ x₁ = 2 ; y₁ = 1
B (-2,-7) ⇒ x₂ = -2 ; y₂ = -7

[tex] \frac{y-y_1}{y_2-y_1}= \frac{x-x_1}{x_2-x_1} \\ \\ \frac{y-1}{(-7)-1}= \frac{x-2}{(-2)-2} \\ \\ \frac{y-1}{(-8)}= \frac{x-2}{(-4)} \\ \\ y-1=(-8). \frac{x-2}{(-4)} \\ \\ y-1=2(x-2) \\ \\ y-1=2x-4 \\ \\ y=2x-4+1 \\ \\ y=2x-3 [/tex]