Question

If the common difference in an arithmetic sequence is 4, and the 20th term is 36, what is the first term?A.-40 B. 76 C. 40 D. 2​

Answer 1

A. - 40

Explanation:

`a_n=a_1+d(n-1)\\\\a_(20)=a_1+d(20-1)\\\\36=a_1+4\cdot19\\\\36=a_1+76\\\\a_1=36-76\\\\a_1=-40`