3корень4*5-корень5=6корень5-корень5=5корень5
2корень4*5-2корень9*5+1=4корень5-6корень5+1=-2корень5+1
1) 1600*40/100=640 г олова
1600-640=960 г меди
2) 100-40=60% меди
3) 640*100/960=200/3≈66,7%
Tg(a + π/4) = (tga + 1) / (1 - tga) = 0.2
0.2*(1 - tga) = tga + 1
0.2 - 0.2tga = tga + 1
-0.8 = 1.2tga
tga = -0.8/1.2
ctga = 1/tga = -1.2/0.8 = 1.5
5a-10b=18;⇒5(a-2b)=18;
(a-2b)=18/5=3.6;
(a²-4b²)/(0.9a+1.8b)=(a-2b)(a+2b)/0.9·(a+2b)=(a-2b)/0.9=3.6/0.9=4;