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Α - угол третьей четверти , значит Cosα < 0
A=lg5,b=lg3
log(a)b=log(c)a/log(c)b
lg2=lg(10/5)=lg10-lg5=1-lg5
log(30)8=lg8/lg30=lg2³/lg(2*3*5)=3lg2/(lg2+lg3+lg5)=
=3(1-lg5)/(1-lg5+lg3+lg5)=3(1-lg5)/(1+lg3)=3(1-a)/(1+b)
Решение
x² - 14x + 45 = 0
D = 196 - 4*1*45 = 196 - 180 = 16
x = (14 - 4)/2 = 5
x = (14 + 4)/2 = 9
<span>x² - 14x + 45 = </span>(x - 5)*(x - 9)