Дано:S2=2;S6=42.Найти знаменатель геометрической прогрессии-q.Помогите пожалуйста

[latex]S_2=2[/latex] [latex]S_6=42[/latex] [latex]q-[/latex] ? [latex]S_n= \frac{b_1*(1-q^n)}{1-q} ,[/latex]  [latex]q \neq 1[/latex] [latex] \left \{ {{S_2= \frac{b_1*(1-q^2)}{1-q} } \atop {{{S_6= \frac{b_1*(1-q^6)}{1-q} } \right. [/latex] [latex] \left \{ {{ \frac{b_1*(1-q^2)}{1-q} =2} \atop {{{ \frac{b_1*(1-q^6)}{1-q}=42 } \right. [/latex] [latex] \left \{ {{ \frac{b_1*(1-q)(1+q)}{1-q} =2} \atop {{{ \frac{b_1*(1-q^3)(1+q^3)}{1-q}=42 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{{ \frac{b_1*(1-q)(1+q+q^2)(1+q^3)}{1-q}=42 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{b_1*(1+q+q^2)(1+q^3)}=42 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{b_1*(1+q)(1-q+q^2)(1+q+q^2)}=42 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{2*(1-q+q^2)(1+q+q^2)}=42 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{2*((1+q^2)^2-q^2)}=42 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{((1+q^2)^2-q^2)}=21 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{1+q^2+2q-q^2}=21 } \right. [/latex] [latex] \left \{ {{b_1*(1+q)} =2} \atop {{1+2q}=21 } \right. [/latex] [latex]1+2q}=21[/latex] [latex]2q}=21-1[/latex] [latex]2q=20[/latex] [latex]q=10[/latex]