The Number Line

The number line — integers from -5 to +5 with zero centered and a distance annotation

Plain English first

A number line is a straight line where every point represents a number. Numbers increase as you move right and decrease as you move left. It never ends in either direction.

The number line gives numbers a location in space — which lets you talk about order, distance, and direction.

The layout

←  ...  -5  -4  -3  -2  -1   0   1   2   3   4   5  ...  →

Zero sits at the center
Positive numbers extend right, growing larger
Negative numbers extend left, growing smaller

Standard math notation

a < b   a is to the LEFT of b  (less than)
a > b   a is to the RIGHT of b (greater than)

Distance between a and b:  |a - b|
Midpoint of a and b:        (a + b) / 2

Verbose Python with descriptive names

def find_position_on_number_line(number):
    """Every number has an exact position — right, left, or at zero."""
    if number > 0:
        return f"{number} is {number} units to the RIGHT of zero"
    elif number < 0:
        return f"{number} is {abs(number)} units to the LEFT of zero"
    else:
        return "0 is AT zero — the center of the number line"


def compute_distance_between_two_points(point_a, point_b):
    """
    Distance is always positive — how far apart, regardless of direction.
    Subtract to find the gap; absolute value removes the sign.
    """
    return abs(point_a - point_b)


def find_midpoint_between_two_numbers(number_a, number_b):
    """The midpoint is exactly halfway — add them and divide by 2."""
    return (number_a + number_b) / 2


# Demonstrations
print(compute_distance_between_two_points(2, 5))    # 3
print(compute_distance_between_two_points(-3, 4))   # 7
print(find_midpoint_between_two_numbers(-4, 4))     # 0.0

Arithmetic as movement

3 + 4 → start at 3, move 4 steps right → 7
3 - 4 → start at 3, move 4 steps left → -1
3 + (-4) → same as subtracting 4 → -1

Common mistakes

Bigger negative ≠ bigger number. -10 is LEFT of -2, so -10 < -2.
Distance is always positive. Distance from 3 to 7 and from 7 to 3 are both 4.
The number line includes everything — fractions, decimals, π all have exact locations.

結果