Question

Calcule a soma dos 5 termos da PG (1/3, 1/15, 4/75)

Answer 1

a1 = 1/3

a2 = 1/15

a3 = 4/75  termo   errado

q = 1/15 :  1/3  ou  1/15 * 3/1 = 3/15 = 1/5 ****

S5 =  a1 .(q^5   -  1 ) / ( q - 1)

S5 =  1/3 [ ( 1/5)^5   -  1 ]  / (  1/5 - 1/1 )

S5 = 1/3 [ ( 1/ 3125) - 1/1  ] / ( - 4/5 )

S5 = 1/3 [ ( - 3124/3125) [ / ( - 4/5 )

S5 =     1/3 *   ( - 3124/3125 ) =  - 3124/ 9375

- 3124/9375 :   ( - 4/5 )  =  ( - 3124/9375 ) *  ( - 5/4 )  = + 15620/37500  

corta  1 zero =   1562/3750 = 781/1875 = ****