D=(а-5)^2-4*2*(a^2-a-20)=-7а^2 -2а+185
-7а^2-2а+185=0
D`=4+4*185*7=5184
а1=(2-72)/(-28)=2,5
а2=(2+72)/(-28)=-2*(4/7)
а1+а2=-1,5
Х= 9
а = 0
в = 4
вот так поучиться.
Sin930° = Sin(90° * 10 + 30) = Cos30° = √3/2
tg31π/6 = tg(5π + π/6) = tgπ/6 = 1/√3
6 3/4х*1 11/45у=27/4х*56/45у=27*56/4*45ху=3*14/1*5ху=42/5ху= 8,4ху
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