(3z²-5)(3z²+5)=9z^4-25;
(y+3)²=y²+6y+9;
(a-5)²=a²-10a+25;
(2b²-1)²=4b^4-4b²+1;
(5+3c²)²=9c^4+30c^2+25;
(c+2)(c²-c+4)=c^3+8;
(y-3)(y²+3y+9)=y^3-27.
(7-6y-4)(7-6y+4)=0
(3-6y)(11-6y)=0
3-6y=0
6y=3
t=0,5
11-6y=0
6y=11
y=11/6
140 - 100%
х - 45%
140/х=100/45
х=140*45/100
х=63
Ответ: 63 учащихся