стр.51 зад4,5 б) и в) (HELP)

[Ivan4oooo23]

ХЕЛП

[ammornil]

Предплагам, че това е задача (4)
[tex]\begin{array}{|l}a_{1}+d=3 \\ a_{1}+2d=5 \end{array} \Leftrightarrow \begin{array}{|l} a_{1}=3-d\\ 3-d+2d=5 \end{array} \Leftrightarrow[/tex][tex]\begin{array}{|l} a_{1}=3-d \\ d=5-3 \end{array} \Leftrightarrow \begin{array}{|l} a_{1}=1\\d=2 \end{array}[/tex]

(5Б)
[tex]\begin{array}{l} a_{4}=a_{1}+3d=-13 \\ a_{7}=a_{1}+6d=-28 \end{array} \Rightarrow a_{7}-a_{4}=a_{1}+6d-(a_{1}+3d) \Leftrightarrow -28-(-13)=a_{1}+6d-a_{1}-3d \Leftrightarrow -15=3d \Leftrightarrow d=-5[/tex]
[tex]a_{7}=a_{1}+6d \Rightarrow a_{1}=a_{7}-6d=-28+30 \Rightarrow a_{1}=2[/tex]

(5В)
[tex]\begin{array}{l} a_{6}=a_{1}+5d=-17 \\ a_{8}=a_{1}+7d=-23 \end{array} \Rightarrow a_{8}-a_{6}=a_{1}+7d-(a_{1}+6d) \Leftrightarrow ...[/tex]