Question

Use the product (a + b) (a – b) = a^2 – b^2 to evaluate: (i) 21 x 19

Answer 1

21×19

= (20+1)(20-1)

= 400-1

= 399

Answer 2

$\underline{\underline{\Huge\mathfrak{Solution ;}}}$

Given ;-
• Evaluate: (i) 21 x 19

According to the Question ;-
$<b>Using the Identity ;- ( a + b ) ( a - b )</b>$

Here,
$<b>Assuming ; a = 20 and b = 1</b>$

Now ,

=> ( 20 + 1 ) ( 20 - 1 )

=> ( 400 - 1 )

=> 399

Hence ,
The answer is $<b>399.</b>$