Question

геометриялык прогрессия

Answer 1

b3=12,b5=48
q²=b5/b3=48/12=4
q=-2 U q=2
b1=b3/q²=12/4=3
b8=b1q^7
b8=3*(-128)=-384 U b8=384

Answer 2

$b_3=12;b_5=47 \\ b_n=b_1q^{n-1} \\ b_8=b_1q^7 \\ b_3=b_1q^2 \\ b_5=b_1q^4 \\ b_1q^2=12;b_1q^4=48 \\ \frac{b_1q^4}{b_1q^2}= \frac{48}{12} \\ q^2=4 \\ g^2-4=0 \\ (q-2)(q+2)=0 \\ q_1=-2\ \textless \ 0 \\ q_2=2\ \textgreater \ 0 \\ q_2=q=2 \\ b_1q^2=12 \\ b_1= \frac{12}{4}=3 \\ b_8=b_1q^7=3*2^7=3*128=384$