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20 12 how to solve the problem of liberal arts mathematics 12 in the new college entrance examination standard?
a2-a 1= 1 ①

a3+a2=3 ②

a4-a3=5 ③

a5+a4=7 ④

a6-a5=9 ⑤

a7+a6= 1 1 ⑥

a8-a7= 13 ⑦

a9+a8= 15 ⑧

a 10-a9= 17 ⑨

……

②-①, ②+③, a3+a 1=2, a4+a2=8, ∴ A1+A2+A3+A4 =/kloc-0.

⑥-⑤,⑥+⑦,a7+a5=2,a8+a6=24,∴a5+a6+a7+a8=26.

In the same way, A9+a10+a1+a12 = 42.

∴s60=a 1+a2+a3+a4+……+a57+a58+a59+a60

=(a 1+a2+a3+a4)+(a5+a6+a7+A8)+……+(a57+a58+a59+a60)= 10+26+42+……

= 15× 10+( 15- 1)* 15/2* 16= 1830

Option d