9х-х³=х(9-х²) или можно так: х(3-х)(3+х)
<span> ctg(pi/12)=koren((1+cos(pi/6))/(1-cos(pi/6)))= </span>
<span>=koren((2+koren(3))/(2-koren(3)))=(2+koren(3))/koren(4-3)=2+koren(3). </span>
sin(75) = cos(90 - 75) = cos(15)
примерно <span>0,9659</span>
tg 15=<span>sin15/cos15</span>
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1)(x^2-3x-2x+6)(x+4)=(x^2-5x+6)(x+4)=x^3-5x^2+6x+4x^2-20x+24=x^3-x^2-14x+24
2)c(7+c+7c+c^2)=c(7+8c+c^2)=7c+8c^2+c^3
3)(3u+u^2-15-5u)(u+9)=(u^2-2u-15)(u+9)=u^3+9u^2-2u^2-18u-15u-135=u^3+7u^2-33u-135
4)(3a+a^2-15-5a)(10+a)=(a^2-2a-15)(10+a)=10a^2+a^3-20a-2a^2-150-15a=a^3+8a^2-35a-150