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1+2sintcost=1+0,44=1,44
sint+cost=+-1,2
1+2sincost=0,16
sintcost=-0,84/2=-0.42
Думаю, максимально подробно
(x - x1)(x - x2) = x^2 - (x1 + x2)x + x1*x2 = x^2 - 5x + 3a
x1 + x2 = 5
x1 * x2 = 3a
x1 = -1
-1 + x2 = 5 -> x2 = 6
x1 * x2 = -1 * 6 = -6 (-> a = -2)