3x^5- 6x³- 21x²- 3x^5+6x³+20x²+x² - 18x - 54=0
- 18x-54=0
- 18x=54
x= - 54:18
x= - 3
(а+б)^2=а^2+2аб+б^2
4а^2+28аб+49б^2
1) ctg (13п/2)=ctg(12п/2 + п/2)=ctg(6п + п/2)=ctg п/2 =0
2) cos (21п/4) = cos(20п/4 + п/4)=cos(5п + п/4) = - cos п/4 = -√2/2
3) sin(41п/4)=sin(40п/4 + п/4)=sin(10п + п/4)=sin п/4= √2/2
4) 5*0+2*(-√2/2)+2*(√2/2)=0-√2+√2=0
Ответ: 0.
2/3 + 7/15 - 2а/12 = 2*20 / 60 + 7*4 / 60 - 2а*5 / 60 =
= 40+28-10а / 60 = 68-10а / 60 = 2(34-5а) / 2*30 = 34-5а / 30
√250=√(25*10)=5√10
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