Question

tinh tong

A=1+7+8+15+23+................+160

help me

Answer 1

 a/A= 1 + 7 + 8 + 15 + 23 +38+ 61+ 99+160 
= 1+ (8-1) + (15-7) + (23-8)+(38-15) + (61-23)+(99-38)+ (160-61) + (259-99) 
= -7 + 160 +259=412 

Answer 2

A=1+7+8+15+...+160

A=1+(8-1)+(15-7)+....+(259-99)

A=-7+160+259=412