Question

Dada a P.A( -33, -29, - 25, -21 determine a15

Answer 1

$(-33;\,-29;\,-25;\,-21;...)$

15º termo:

$a_1 = -33 \\ r = 4 \\ a_{15} = \,? \\ \\ a_n = a_1+(n-1)r \\ \\ a_{15} = -33+(15-1)\cdot4 \\ \\ a_{15} = -33 + 14\cdot4 \\ \\ a_{15} = -33 + 56 \\ \\ \boxed{a_{15} = 23}$