In the figure given below, $DE$ is the diameter of a circle. So, express the diameter of the circle in terms of its radius.

The equal sides of an isosceles triangle is $a$ and that of the unequal side is $b$. Express the general rule for the perimeter of the isosceles triangle.

The order in which two numbers are added will not change their sum. This property is known as the commutative property of addition. Express this property in a general way by using variables. 

If zero is added to a number or a number is added to zero, then the result is the number itself. Generalise this property of numbers using a variable. 

The order in which three numbers are multiplied will not change their product. Express the property in a general way using variables $x, y \text{and} z$.

State whether given expression is arithmetic expression or not:

$z-9$

State whether given expression is arithmetic expression or not:

$7+\left(9\times 8\right)$

State whether given expression is arithmetic expression or not:

$6$

State whether given expression is arithmetic expression or not:

$4\times 8-9+x$