1/2*sin150*tg75=1/2*sin30*tg75=1/4*tg75=1/4*tg(45+30)=
=1/4*(tg45+tg30)/(1-tg75*tg30)=1/4*(1+1/√3)/(1-1/√3)=
=1/4*(√3+1)²/(√3-1)(√3+1)=1/4*(3+2√3+1)/(3-1)=1/4*(4+2√3)/2=
=1/4*2(2+√3)/2=(2+√3)/4
(m-5)^2=m^2-10m+25
(-m+5)^2=m^2-10m+25
(-m-5)^2=m^2 +10m+25
(c^3-1)^2=c^6-2c^3+1
(p^3-q^3)^2=p^6-2p^3q^3+q^6
(x^2-y)^2=x^4-2x^2y+y^2
(a^2-1)^2=a^4-2a^2+1
21.а) x^2-14x+24=0; D=196-96=10^2; x1=(14+10)/2=12; x2=(14-10)/2=2;
21.б) -x^2+17x+45=0; D=289+180=469; x1=(17+Корень из 469)/2; x2=(17-Корень из 469)/2.
22.а) 2x^3+3x+1=0; D=9-8=1; x1=(-3+1)/4=-0.5; x2=(-3-1)/4=-1;
22.б) 5x^2-8x+3=0; D= 64-60=4; x1=(8+2)/10=1; x2=(8-2)/10=0.6
Cosx(cos^2x-sin^2x-1)=0;
cos^3x-cosx(1-cos^2x)-cosx=0;
cos^3x-cosx+cos^3x-cosx=0;
2cos^3x-2cosx=0;
2cosx(cos^2x-1)=0;
2cosx=0;
x=π/2+πk;
cos^2x=1;
cosx=+-1;
x=+-πk;