<span> (y-3)(y+5)= у^3+5y-3y-15=y^3+2y-15</span>
(sin a) / (1-cos a) - (1+cos a)/(sin a)=0 ((sin^2 a) -(1-cos a)*(1+cos a)) /((1-cos a)*(sin a)) =0 ((sin^2 a)-1+(cos^2 a)) /((1-cos a)*(sin a)) =0 (1-1) /((1-cos a)*(sin a)) =0 0 /((1-cos a)*(sin a)) =0 0=0, доказано.
-12 х= 3/5
х= 3/5 : (-12)
х= -1/20
(x+3)^2-x^2 x=-3 (-3+3)^2-(-3)^2=0^2-9=-9