<span>Общее количество карандашей=ab+by</span>
1)y '=6x^5
2)y '=0
3)y '= -5/x^2
4)y '=-5
5)y '=8/2√x-0.5sinx=4/<span>√x-0.5sinx
6)y '=(sinx) '*x-sinx*(x) ' /x^2=cosx^2-sinx/x^2
7)y '=(x) '*ctgx+(ctgx) '*(x)=ctgx-x/sin^2x
</span>
![\left \{ {{3x-6\ \textgreater \ 0} \atop {5-x \leq 0}} \right.\\\\ \left \{ {{3x\ \textgreater \ 6} \atop {-x \leq -5}} \right.\\\\ \left \{ {{x\ \textgreater \ 2} \atop {x\ \textgreater \ 5}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7B3x-6%5C+%5Ctextgreater+%5C+0%7D+%5Catop+%7B5-x+%5Cleq+0%7D%7D+%5Cright.%5C%5C%5C%5C+%5Cleft+%5C%7B+%7B%7B3x%5C+%5Ctextgreater+%5C+6%7D+%5Catop+%7B-x+%5Cleq+-5%7D%7D+%5Cright.%5C%5C%5C%5C+%5Cleft+%5C%7B+%7B%7Bx%5C+%5Ctextgreater+%5C+2%7D+%5Catop+%7Bx%5C+%5Ctextgreater+%5C+5%7D%7D+%5Cright.+++)
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2 5
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x ∈ [5 ; + ∞)
Ответ: 5