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Исходное не пишу
<em>х²</em>+18х+81+<em>х²</em>-22х+121<em>-2х²</em>=0
-4х=-202
х=50,5
корень один
cos15° = cos(45° - 30°) = cos45° · cos30° + sin45° · sin30° =
= √2/2 · √3/2 + √2/2 · 1/2 = √6/4 + √2/4 = (√6 + √2)/4
(a√a-b√b)/(a-b)=(√a-√b)(a+√(ab)+b)/(√a-√b)=a+√(ab)+b
a=0,2 b=0,8
0,2+√0,16=0,8=1+0,4=1,4