Question

$<b><font face=Copper black size=4>$Evaluate :

1) {(405)² - (395)²}

2) {(7.8)² - (2.2)²}

Answer 1

$\huge\boxed{\texttt{\fcolorbox{green}{aqua}{Hey Mate!!!}}}$

$<b><i>$1) (405 + 395) (405 - 395)

= 800 × 10

= 8000

2) (7.8 + 2.2) (7.8 - 2.2)

= 10 × 5.6

= 56

Answer 2

$<b> <i> Here's the answer$

$1. {(405) }^{2} - (395) {}^{2}$

Using the identity,

$a ^2 + b ^2 = ( a + b ) (a - b)$

$\sf{\therefore(405 + 395) \times (405 - 395)}$

$\sf{= 800 \times 5}$

$\sf{= 4000}$

Now,

Similarly,

In second question,

$\sf{2. \: \: {(7.8) {}^{2} } - (2.2) {}^{2}}$

$\sf{{(7.8 + 2.2)} \times (7.8 - 2.2)}$

$\sf{ = 10 \times 5.6}$

$\sf{ = 56}$

Thanks!!