Question

tinh nhanh 

21^2=

199^2=

299.301=

31^2=

99^2=

62.58=

Answer 1

21² = ( 20 + 1 )² = 20² + 2.20.1 + 1² = 400 + 40 + 1 = 441

199² = ( 200 - 1 )² = 200² - 2.200.1 + 1² = 40 000 - 400 + 1 = 39 601

299.301 = ( 300 - 1 )( 300 + 1 ) = 300² - 1² = 90 000 - 1 = 89 999

31² = ( 30 + 1 )² = 30² + 2.30.1 + 1² = 900 + 60 + 1 = 961

99² = ( 100 - 1 )² = 100² - 2.100.1 + 1² = 10 000 - 200 + 1 = 9801

62.58 = ( 60 + 2 )( 60 - 2 ) = 60² - 2² = 3600 - 4 = 3596

Answer 2

199² = (200 – 1)² = 200² – 2.200 + 1 = 40000 – 400 + 1 = 39601