А^2б^3-а^3б^4=а^2б^3(1-аб)
=====================$$
<span>x^2-3(6-x)^2=4
x^2-3(36-12x+x^2)=4
x^2-108+36x-3x^2=4
-2x^2+36x-112=0(/(-2)
x^2-18x-56=0
D=324-224=100
корень из D=10
x1=18-10/2=4
x2=18+10/2=14
Ответ:4,14</span>
24
(ctg²2a-1)/2ctg2a -cos8a*ctg4a=ctg4a-cos8a*ctg4a=
=ctg4a*(1-cos8a)=cos4a/sin4a *2sin²4a=2sin4a8cos4a=sin8a
25
(sin^4a-cos^4a+cos²a)/2(1-cosa)=
=[(sin²a+cos²a)(sin²a-cos²a)+cos²a]/2(1-cosa)=
=(sin²a-cos²a+cos²a)/2(1-cosa)=sin²a/2(1-cosa)=
(1-cos²a)/2(1-cosa)=(1-cosa)(1+cosa)/2(1-cosa)=(1+cosa)/2=
=2cos²(a/2)/2=cos²(a/2)