Question

 Cho A + B = 12. Tính các tổng sau:

a, 

b, 

Answer 1

a) 13 x A + 5 x B + 13 x B + 5 x A

= ( 13 x A + 13 x B ) + ( 5 x B + 5 x A )

= 13 x ( A + B ) + 5 x ( B + A ) mà A + B = 12 

=> 13 x ( A + B ) + 5 x ( B + A ) 

= 13 x 12 + 5 x 12

= 12 x ( 13 + 5 )

= 12 x 18 

= 216

b) 4 x A + 25 x B + 16 x A - 5 x B

= ( 4 x A + 16 x A ) + ( 25 x B - 5 x B )

= A x ( 4 + 16 ) + ( 25 - 5 ) x B

= A x 20 + 20 x B

= 20 x ( A + B ) mà A + B = 12 

=> 20 x ( A + B )

= 20 x 12

= 240

Answer 2

Trả lời :

a) 13 x A + 5 x B + 13 x B + 5 x A

= 13 x (A + B)+  5 x (A + B)

= (13 x 12) + (5 x 12)

= 156 + 60

= 216

b) 4 x A + 25 x B + 16 x A - 5 x B

= 25 + 4 x (A + B) + 16 - 5 x (A + B)

= 29 x 12 + 11 x 12

= 348 + 132

= 480

T i c k nha !!