Найти четвертый член геометрической прогрессии, если B2=- 2, B7 =1/16

[tex]b_2=-2[/tex]
[tex]b_7= \frac{1}{16} [/tex]
[tex]b_4-[/tex] ?

[tex] \left \{ {{b_1*q=-2} \atop {b_1*q^6= \frac{1}{16} }} \right. [/tex]
[tex] \left \{ {{b_1*q=-2} \atop {b_1*q*q^5= \frac{1}{16} }} \right. [/tex]
[tex] \left \{ {{b_1*q=-2} \atop {-2*q^5= \frac{1}{16} }} \right. [/tex]
[tex] \left \{ {{b_1*q=-2} \atop {q^5= -\frac{1}{32} }} \right. [/tex]
[tex] \left \{ {{b_1=- \frac{2}{q} } \atop {q= -\frac{1}{2} }} \right. [/tex]
[tex] \left \{ {{b_1=4} \atop {q= -\frac{1}{2} }} \right. [/tex]

[tex]b_4=b_1*q^3=4*(- \frac{1}{2} )^3=4*(- \frac{1}{8} )=-0.5[/tex]

Ответ: -0.5