(4+√7) / (√7+1)²=(4+√7)/(7+2√7+1)=(4+√7)/(8+2√7)=<span>(4+√7)/2(4+√7)=1/2</span>
=х^2-18х-81=х^2-3х-9; х^2-18х-81-х^2+3х+9=0; -18х-81+3х+9=0; -15х-72
Решение
(1/2)arccos(-√3/2) - 4arcsin(-√2/2) = (1/2)/(5π/6) - 4*(- π/4) =
= 5π/12 + π = 17π/12
4a*(-3b)=-12ab
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