Пліз! Знайти кут між прямим х+у+1=0 і 7х+5у-1=0

[latex]\left \{ {{x+y+1=0} \atop {7x+5y-1=0}} \right.<=>\left \{ {{x=-y-1} \atop {7(-y-1)+5y-1=0}} \right.<=>\left \{ {{x=-y-1} \atop {-7y-7+5y-1=0}} \right.<=>\\\ \\\ <=>\left \{ {{x=-y-1} \atop {-2y=8}} \right.<=>\left \{ {{x=-y-1} \atop {y=-4}} \right.<=>\left \{ {{x=-(-4)-1} \atop {y=-4}} \right.<=>\\\ \\\ <=>\left \{ {{x=3} \atop {y=-4}} \right.[/latex]