Final answer:
The original question seems to ask for substitution of values into undefined expressions. However, the related examples focus on scientific notation and significant figures, which involve expressing numbers in a specific format and with a certain level of precision according to the given values and calculations.
Step-by-step explanation:
The question seems a bit fragmented, so I'll clarify the mathematics problem at hand. The question might be asking to solve expressions given certain variable values — ‘a’ and ‘b’. However, the examples given from different exercises relate to scientific notation and significant figures. Therefore, without the exact expressions in which to substitute a=5, and b=21, it is not possible to solve them directly. As such, we'll explore some of the mathematical exercises mentioned.
Scientific Notation Exercises
Scientific notation is a way of expressing numbers that are too large or too small to be conveniently written in decimal form. In this case, for example:
Exercise 2.4.2 (a): To find the scientific notation of the division 217 ÷ 903, we first perform the division to find the value and then express this in scientific notation.
Exercise 2.4.4 (a): To find the product of 22.4 x 8.314, we multiply the numbers and then format the result into scientific notation, making sure to use the correct number of significant figures.
Exercise 1.9.2 (d): To find the product of 0.00666 × 321, we carry out the multiplication and then express it in scientific notation.
Remember, when dealing with scientific notation and significant figures, accuracy and adherence to mathematical rules are crucial. Proper significant figures depend on the precision of the numbers you are given and the operations you perform.