Ответ тут....................................
Cos(2x -π/2) = 0 ;
2x -π/2 = π/2+π*k , k ∈Z ;
2x = π + π*k , k ∈Z ;
x = π(1 +k)/2 , k ∈Z .
№1
а)(x-7)²+3=(x-2)(x+2)
x²-14x+49+3=x²+2x-2x-4
-14x=-56
x=3
б)(x+6)²-(x-5)(x+5)=79
x²+12x+36-x²-5x+5x+25=79
12x=18
x=1,5
№2
a)(а+5)(а ²-5а+25)-125=a³-5a²+25a+5a²-25a+125-125=a³<span>
б)</span><span>27+(с-3)( с ²+3с+9) =27+c</span>³+3c²+9c-3c²-9c-27=c³
8х-68у+68у-13=8х-13
8х=13
х=13/8