Question

determinar o vigesimo termo da PA(1,8,15)

Answer 1

r = a2 - a1

r = 8 - 1

r = 7



a20 = a1 + 19r

a20 = 1 + 19 * 7

a20 = 1 + 133

a20 = 134

Answer 2

$\mathsf{ a_n=a_1+(n-1)\cdot r}$

$\mathsf{a_{20}=1+(20-1)\cdot7 }$

$\mathsf{ a_{20}=1+19\cdot 7}$

$\mathsf{a_{20}=1+133 }$

$\boxed{\boxed{\mathsf{a_{20}=134}} }$