( 2 3/4+2 1/5)*16=(2 15/20+2 4/20)*16=4 19/20 * 16=4*16 + 19/20*16=64+76/5=94 1/5
9a^4-72a=9a(a^3-8) - вынос общего множителя.
9а^4-72a=9a(a-2)(a^2+a+2)
Корни уравнения равны
![x= \frac{-2p+ \sqrt{ (2p)^{2}-4*3*5 } }{6} =\frac{-2p+ \sqrt{ (2p)^{2}-60 } }{6}](https://tex.z-dn.net/?f=x%3D+%5Cfrac%7B-2p%2B+%5Csqrt%7B+%282p%29%5E%7B2%7D-4%2A3%2A5+%7D+%7D%7B6%7D+%3D%5Cfrac%7B-2p%2B+%5Csqrt%7B+%282p%29%5E%7B2%7D-60+%7D+%7D%7B6%7D)
и
![x= \frac{-2p- \sqrt{ (2p)^{2}-4*3*5 } }{6} =\frac{-2p- \sqrt{ (2p)^{2}-60 } }{6}](https://tex.z-dn.net/?f=x%3D+%5Cfrac%7B-2p-+%5Csqrt%7B+%282p%29%5E%7B2%7D-4%2A3%2A5+%7D+%7D%7B6%7D+%3D%5Cfrac%7B-2p-+%5Csqrt%7B+%282p%29%5E%7B2%7D-60+%7D+%7D%7B6%7D)
если
![\sqrt{ (2p)^{2}-60} = 0,](https://tex.z-dn.net/?f=+%5Csqrt%7B+%282p%29%5E%7B2%7D-60%7D+%3D+0%2C+)
то корень один
![x= \frac{-2p }{6}](https://tex.z-dn.net/?f=x%3D+%5Cfrac%7B-2p+%7D%7B6%7D+)
если
![(2p)^{2}-60\ \textless \ 0](https://tex.z-dn.net/?f=%282p%29%5E%7B2%7D-60%5C+%5Ctextless+%5C+0)
, то корней нет
если
![(2p)^{2}-60\ \textgreater \ 0, 4 p^{2} \ \textgreater \ 60, p^{2} \ \textgreater \ 15](https://tex.z-dn.net/?f=+%282p%29%5E%7B2%7D-60%5C+%5Ctextgreater+%5C+0%2C+4+p%5E%7B2%7D+%5C+%5Ctextgreater+%5C+60%2C++p%5E%7B2%7D+%5C+%5Ctextgreater+%5C+15)
, p∈(-∞; -√15)∪(√15; +∞), то 2 корня
10 не сделал. Возможно там опечатка.