Алгебра Розв'язати систему рівнянь трьома
8 клас​

1) y = 4 cos x + 27 x/π   + 3;
y'(x) = - 4 sin x + 27/π;
y;(x) = 0;
- 4 sin x + 27/π = 0;
 - 4 sin x = - 27/π;
 sin x = 27/4π;
π≈3,14;
27/4π≈27/12,48 >1;
-1 ≤ sin x ≤ 1;   нет решений, то есть нет стационарных точек.
Проверим значения функции на концах заданного интервала.
f(- 2π/3) = 4 cos(-2π/3 ) + 27 (-2π/3) / π + 3=
=4*(-1/2) - 18 + 3= - 17.
f(0) = 4 cos 0 - 27*0/π  + 3 = 4*1 - 0 + 3 = 7;
f(0) > f(- 2π/3);
ответ  :  f(наим.)=f(- 2π/3)= - 17.
2) y =  5 sin x - 36x /π + 6;
y'(x)= 5 cos x - 36/π;
 y;(x) = 0;
 5 cos x - 36/π=0;
5 cos x = 36/π;
 cos x = 36 / 5π≈2,2;
 - 1 ≤ cos x ≤ 1; нет решений, то есть нет стационарных точек.
Проверим значения функции на концах заданного интервала.
f(- 5π/6) = 5*sin(- 5π/6) - 36(-5π/6)+6 =5*(-1/2)+ 30+6=
=33,5.
f(0) = 5 sin 0 - 36*0/π + 6 = 5*0 - 0 + 6 = 6.
f(0) < f(- 5π/6) ; 
f(наиб.) = f(- 5π/6)= 33,5

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