Simple example of normalized delta x and y values.

main.lua

function love.load()
    local start_x = 0
    local start_y = 0
    local end_x = 10
    local end_y = 5

    dx = (end_x - start_x)
    dy = (end_y - start_y)

    local distance = math.sqrt(dx^2 + dy^2)

    x = start_x
    y = start_y

    dx = dx / distance
    dy = dy / distance
end

function love.update(dt)
    local speed = 100 * dt
    x = x + dx * speed
    y = y + dy * speed
end