См скриншоты
=================================
2x^2-2x+4x^2+8x-6x-12=6x^2-12
<em>sinα=-√(1-cos²α)=-√(1-16/25)=-3/5</em>
<em>tgα=sinα/cosα=(-3/5):(-4/5)=</em><em>3/4</em>
<em />
( 5+√7)²+(5-√7)² = 25+10√7+7+25-10√7 +7 = 50+14 = 64
7x^2+20x-3=0
a=7, b=20, c=-3
D=b^2-4ac
D=400-4*7*(-3)=400+84=484
x1=(-20+22)/14=1/7
х2=(-20-22)/14=3
<u>х1= 1/7</u>, <u>х2=3</u>