trygonometria Freak:

	1		π
oblicz cos(α+β), jeśli sinαsinβ=		oraz α−β=
	2		2

wredulus_pospolitus: zauważ, że: cosα = cos(β + (α−β)) = cos(β + π/2) = −sinβ sinα = sin(β + (α−β)) = sin(α + π/2) = cosβ czyli: cos(α+β) = cosαcosβ − sinαsinβ = −sinβ*sinα − sinαsinβ = −2sinαsinβ = −2*(1/2) = −1