A symbol, usually a letter, that represents an unknown quantity is called a .

A variable is a symbol that represents an unknown or changeable number, typically a letter such as x, y, and z.

Step-by-step explanation:

a symbol, usually a letter, that represents an unknown quantity is called x.

Step-by-step explanation:

constant acceleration- a

constant velocity- c

no velocity or acceleration- b

explanation:

for body moving with a constant acceleration, the rate of change of displacement changes over time. this is proven by the increasing gradient of the curve (a) against time.

a body that is moving at constant velocity covers equal distances over equal periods of time, thus the straight line with a constant gradient c.

a stationary body   covers no displacement as time elapses. thus the flat line with   zero gradient.