Question

Tính nhẩm:

a) \(26^2+52.24+24^2\)

b) \(3003^2-3^2\)

c) \(87^2+73^2-27^2-13^2\)

d) \(79^2-79.58+29^2\)

Answer 1

a) 26² + 52.24 + 24²
= 26² + 2.26.24 + 24²
= ( 26 + 24 )²
= 50² = 2500
b) 3003² - 3^2
= ( 3003 + 3 ) ( 3003 - 3 )
= 3006 . 3000 = 9018000
c) 87² + 73² - 27² -13²
= ( 87² - 13² ) + ( 73² - 27² )
= [ ( 87 + 13 )( 87- 13 )] + [ ( 73 - 27 )( 73 + 27 ) ]
= ( 100 . 74 ) + ( 46 . 100 )
= 7400 + 4600 = 12000
d)79² - 79.58 + 29²
= 79² - 2.79.29 + 29²
= ( 79 - 29 )²
= 50² = 2500

Answer 2

a) 26² + 52 . 24 + 24² = 26² + 2 . 26 . 24 + 24²

= ( 26 + 24 )²

= 50²

= 2500

b) 3003² - 3² = ( 3003 - 3 ) . ( 3003 + 3 )

= 3000. 3006

= 9018000

c) 87² + 73² - 27² - 13² = ( 87² - 27² ) + ( 73² - 13² )

= ( 87 - 27 ) . ( 87 + 27 ) + ( 73 - 13 ) . ( 73+13)

= 60 . 114 + 60 . 86

= 60 . ( 114 + 86 )

= 60 . 200

= 12000

d) 79² - 79 . 58 + 29² = 79² - 2 . 79 . 29 + 29²

= ( 79 - 29 )²

= 50²

= 2500