Question

Resolva a equação (X + 1)+ (X+3)+(X+5)+.... +(X+39)=620

Answer 1

n = 20
a1 = x + 1
a1n = x + 39
a2 = x + 3
r = ( x + 3) - ( x + 1)  = x + 3 - x - 1 = 2 ***

620 = ( x + 1) + ( x + 39).10
620 =( 2x + 40)10
620/10  = 2x + 40
62 = 2x + 40
62 - 40 = 2x
22 = 2x
x = 11 ***