Wiedząc, że sin alfa + cos alfa=1,3, oblicz sin alfa * cos alfa. Bardzo proszę o pomoc. Dam naj :)

[latex]sinalpha+cosalpha=1.3; |^2[/latex] [latex](sinalpha+cosalpha)^2=1.69[/latex] [latex]sin^2alpha+2sinalphacosalpha+cos^2alpha=1.69[/latex] [latex]sin^2alpha+cos^2alpha+2sinalphacosalpha=1.69[/latex] [latex]1+2sinalphacosalpha=1.69[/latex] [latex]2sinalphacosalpha=0.69[/latex] [latex]sinalphacosalpha=dfrac{0.69}{2}[/latex] [latex]oxed{sinalphacosalpha=0.345}[/latex]