1
tg23*tg(270+23)+sin52*sin(180-52)-sin(270+52)*sin(90+52)=
=tg23*(-ctg23)+sin52*sin52+cos52*cos52=-1+sin²52+cos²52=-1+1=0
2
<span>(1-2sin²13°) × cos64° / (2cos²19° - 1)=cos26*sin26/cos38=
=(sin52)/2cos(90-52)=(sin52)/2sin52=1/2</span>
63,55 = 63( 1 - Х ) + 65х
63,55 = 63 - 63х + 65х
63,55 = 63 + 2х
2х = 0,55
Х = 0,275
-7x² - 2x + 1 = 0 ⇔ 7x² + 2x - 1 = 0
D= 4 + 4*7 = 32, √D = √32 = 4√2
x₁ = (-2 + 4√2) / 14 = (-1 + 2√2) / 7
x₂ = (-2 -4√2) / 14 = (-1 - 2√2) / 7
x₁ * x₂ = (-1 + 2√2) * (-1 - 2√2) / 49 = - 7 / 49 = - 1/7