Expansion of (x + a) (x +b)

Expansion of (x + a) (x +b)

          Which two quantities are to be multiplied ? (x +a) and (x + b). which is the equal term in (x + a) (x + b) ?      ……….. x.

          Which are the unequal terms in the quantities (x + a) and                        (x + b) ?                                       ……. a and b

          Study the following multiplication shown in horizontal arrangement.

(x + a) (x + b)       = x × (x + b) + a × (x + b)

                             = x² + xb + ax + ab

                             = x² + ax + bx + ab

                             = x² + (a + b)x + ab

Which are the terms in the product ?    ……x², (a+b)x and ab

What is the characteristic of the first term ?

………… square of the equal term.

What is the characteristic of the second term ?

…… Sum of the two unequal terms multiplied by the equal term.

What is the characteristic of the third term ?

……..product of the unequal terms.

This can be written in words as follows.

(equal term + first unequal term) (equal term + second unequal term)

= (equal term)² + (sum of unequal terms) × (equal term) + (product of unequal terms)

This gives us the following formula.

(x+a) (x+b) = x² + (a+b)x  + ab

Irrational and Real Numbers

Irrational and Real Numbers

Revision : Rational numbers

         

 The numerators in the numbers , , ,  are integers while their denominators are non-zero integers. Hence, these are rational numbers. If p is any integer and q, any non-zero integer, then,  is a rational number

The decimal form of a rational number

          

Two rational numbers can have different decimal forms. To understand the nature of this difference, let us work out the decimal form of two rational numbers  and , and study them. What is the difference in the decimal forms ?

(1)  The decimal form of .

The decimal form of  is 7.9375

As the remainder in this example is 0, the process of division is complete. Hence, we do not get any digit after 5 in the quotient obtained.

          It means that the decimal form 7.9375 is a terminating one. 

Square roots of numbers

Square roots of numbers

          It is customary not to write ‘+’ sign before a positive number. For example, +10 = 10. 

We shall, henceforth, observe this convention in all discussions.

6 ×  = 36     ∴ 6 is the square root of 36.

Similarly, (-6) × (-6) = 36       ∴ (-6) too is a square root of 36.

          
Thus, 6 and -6 are the two square roots of 36.

         

study the following video lessons:

 In the same way, work out in your mind the pairs of numbers of which 4, 49 and 121 are the squares and write statements like the above.

          What do we learn by observing the numbers and their square roots in the above examples?
we see that –

* Every positive number has two square roots.

* These square roots are opposite numbers of each other.