A formula for finding the first term of arithmetic sequence

A formula for finding the first term of arithmetic sequence

an=a1-（n-1）d
An is n, A1 is the first, D is the tolerance

1. Given a, B, find the cosine value:
（1）a=（3,4）,b=（-2,5）
（2）a=（-2,-3）,b=（1,2）

1) | vector a | = √ (3 ^ 2 + 4 ^ 2) = 5 | vector B | = √ [(- 2) ^ 2 + 5 ^ 2] = √ 29 vector A. vector b = (3,4). (- 2,5) = - 6 + 20 = 14, so cos = (vector a. vector b) / (| vector a | vector B |) = 14 / (5 * √ 29) = 14 √ 29 / 145 (2) cos = (A.B) / (| a | B |) = - 8 / (√ 13 * √ 5) = - 8 √ 65 / 65

Chinese and English in Vocational High School
Is math, Chinese and English in Yancheng vocational high school the same as Kunshan?

It's different