Question

Using suitable identity, evaluate : 399 × 401.

Answer 1

(399) × (401 )

= ( 400 - 1 ) × (400 + 1)

= ( 400) ^2 - (1)^2

= 160001

Answer 2

$\huge{\rm{\orange{answer-}}}$

$\huge{ \boxed{ \rm{ \red{identity}}}}$

399 × 401 = (400 - 1)(400 + 1)

(a + b)(a - b) = a² - b²

$\red{a\:=\:400\:,\:b\:=1}$

= 400² - 1²

= 160000 + 1

$\green{=\:160001}$

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