9х^2-12x-6x+8=6x^2-2x+9x-3+3x^2-12x+x-4
9x^2-18x+8=9x^2-5x-7
-18x+5x=-8-7
-13x=-15
x=15/13
1)x^2-7x+2=0
a=1
b=-7
c=2
Дискриминант=b^2-4ac=49-8=41
x1=7+√41/2
x2=7-√41/2
2)х^2-х-30=0
a=1
b=-1
c=-30
Дискриминант=1+120=121
х1=1+11/2=6
х2=1-11/2=-5
Y=2x-5 y'=2
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Ctg²t·(cos²t-1)+1=ctg²t·(-(1-cos²t))+1=ctg²t·(-sin²t)+1=(cos²t/sin²t)·(-sin²t)+1=
=-cos²t+1=sin²t