Question

Clasa a 9 a.Test 2 exercitii la matematica,urgent,ajutor.Multumesc!​

Answer 1

Răspuns:

Explicație pas cu pas:

1a) S100 = (a1+a100)/2

S100 = (10+150)/2 = 160/2 = 80

b) S100 = (5,5+7,5)/2 = 13/2

c) a100 = a1 + 99*r = 2 + 99(-5) = 2 -495 = -493

S100 = (2 -493)/2 = -491/2

d) a100 = -1 + 99*1 = -1 + 99 = 98

S100 = (-1 + 98)/2 = 97/2

2a) Sistem:

c5  = a1 + 4r = 27 ; a1 = 27 - 4r

c27 = a1 + 26r= 60 ; 27-4r+26r= 60 ; 22r = 33 ;  

r = 3/2   ; a1 = 27 - 4*3/2 = 27 - 6 = 21

d) a1 + a1+6r = 42      ; 2*a1 + 6r = 42 |:2

  a1 + 9r -(a1-2r) = 21 ; 7r = 21 ;  r = 3

2*a1 + 6r = 42 |:2

a1 + 3r =21 ; a1 + 9 = 21 ;  a1 = 12

Restul singur(a), model 2a)