Question

Quantos termos tem a PA (-35, -30, -25, ... 125)?

Answer 1

$r=a_{2} -a_{1} =-30-( -35) \Longrightarrow r=5 \\ \\ a_{n} =a_{1} +( n-1) r \\ \\ \Longrightarrow 125=-35+( n-1) \cdotp ( 5) \\ \\ \Longrightarrow 5n-5=160 \\ \\ \Longrightarrow 5n=165 \\ \\ \Longrightarrow n=33$