Răspuns:
Explicație pas cu pas:
1.
b2 = b1*q
20 = 4*q
q = 20 : 4 = 5
b3 = b2*q = 20*5 = 100
b4 = b3*q = 100*5 = 500
2.
b1 = -1/2
b2 = b1*q
b3 = b1*q^2
b4 = b1*q^3
(-1/2)*q^3 = -4
q^3 = -4 : (-1/2) = 8 = 2^3
q = 2
b1 = -1/2
b2 = -1/2*2 = -1
b3 = -1*2 = -2
b4 = -2*2 = -4
b5 = -4*2 = -8
b6 = -8*2 = -16
b7 = -16*2 = -32
b8 = -32*2 = -64
S8 = -1/2 - 1 -2 -4 - 8 - 16 - 32 - 64 = -1/2 - 127 = -127,5
______________________
b5 = -7250
q = 5
b5 = b1*q^4
-7250 = b1*5^4 = b1*625
b1 = -7250 : 625 = -11,6
b10/b7 = b1*q^9/b1*q^6 = q^3 = 5^3 = 125
________________________
q = 2
S5 = b1 + b2 + b3 + b4 + b5
= b1 + b1*q + b1*q^2 + b1*q^3 + b1*q^4
= b1*(1 + q + q^2 + q^3 + q^4)
31√3 = b1*(1 + 2 + 4 + 8 + 16) = b1*31
b1 = 31√3 : 31 = √3
b7 = b1*q^6 = √3 * 2^6 = 64√3
b1 + b2 = √3 + 2√3 = 3√3
