Question

calcule a soma dos 30 primeiros termos da PA (4, 10...)

Answer 1

$S_{30}=\dfrac{(a_1+a_{30})30}{2}=15(a_1+a_{30})$

$a_1=4$

$r=10-4=6$

$a_{30}=4+29\cdot6=4+174=178$

$S_{30}=15\cdot(4+178)=15\cdot182=2~730$

Answer 2

Sn = ( a1 + an ) * n /  2  
Sn = ( 4 + 178 )  *  30 /  2   
Sn = 182 . 15  
Sn = 2.730