Answer:
a = 3
Step-by-step explanation:
Calculate the distance d using the distance formula and equate to 4
d = [tex]\sqrt{(x_{2}-x_{1})^2+(y_{2}-y_{1})^2 }[/tex]
with (x₁, y₁ ) = (2, - 1) and (x₂, y₂ ) = (2, a)
d = [tex]\sqrt{(2-2)^2+(a+1)^2}[/tex] = [tex]\sqrt{0+(a+1)^2}[/tex] = [tex]\sqrt{(a+1)^2}[/tex] = a + 1 then
a + 1 = 4 ( subtract 1 from both sides )
a = 3
