Y=(2/5)x-1 y=0,4x-1
<span>4x-10y=10, y=0,4x-1
графики этих уравнений совпадают</span>
Cos(pi/2+x) = -sinx
cos2x= cos^2x - sin^2x
-sinx = cos^2x - sin^2x
cos^2x =1 - sin^2x
-sinx = 1-sin^2x - sin^2x
2sin^2x - sinx - 1 =0
sinx = t
2t^2-t-1=0
D = 1 + 8 = 9
t1 = 1+3/4 = 4/4 = 1
t2 = -2/4 = -0.5
sinx = 1
x = pi/2+2pin
sinx = -0.5
x = -pi/6+2pin
x = -5pi/6+2pin
sin (-a) = -sin(a) cos (-a) = cos(a)
табличные значения:
sin(-30) = -sin(30) = -1/2
cos(30) = V3 / 2
cos(-45) = cos(45) = V2 / 2 = sin(45)
tg(30) = V3 / 3 = ctg(60)
а теперь подставим...
... = (-1/2 - V3 / 2)^2 / (3*2/4 - 6*3/9) = (-1-V3)^2 / 4 * (-2) = (1+2V3+3)/(-2) = -2 - V3