(1-cosa)(1+cosa)/sin²(-a)=(1-cos²a)/sin²a=sin²a/sin²a=1
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sin(-a)*sin(-a)=-sina*(-sina)=sin²a
3)= 3с6/а2
4)=2ab-(a2+2ab+b2)+2a2=2ab-a2-2ab-b2+2a=a2-b2=(a-b)(a+b) Д. Т.
5)x2(x+3)-9(x+3)=0
(x+3)*(x2+9)=0
x+3=0 x=-3
x2-9=0 x=±3
x=3,x=-3
4х(х+3)=4-3х 4х²+12х=4-3х. 4х²+12х-4+3х=0. 4х²+15х-4=0. Д: 225+64= 289 = 17² х1 = (-15+7):8= -1; х2= (-15-7):8 = -2.75