1) х1+х2=-b/a
b1=2.5;
b4=20;
bn=b1*q^(n-1);
b4=b1*q^3;
q^3=b4/b1;
q^3=20/2,5;
q^3=8;
q=2;
b2=2,5*2=5;
b3=5*2=10;
√2sin22,5 cos22,5 = 2·sin22,5 cos22,5 · √2/2 = sin45°· √2/2 = √2/2·√2/2 = 1/2
2) 3sin2x-2cosx=0