Question

Tính nhanh

a) 4+4+8+12+20+...+356+576

b) 1+3+5+9+17+31+...+293+455

Answer 1

Quy luật đơn giản thôi

a, 4 + 4 + 8 + 12 +20 +.. +576 

ST3 =ST2 +St1

St 4 = st 3 +st2

......

b, St4 =st3 +st2 +st1

  st5 = st4 + st3 +st2 

......

Answer 2

I don't know how fast it is. I just know how to calculate slowly