(с-6)^2–(7+с)^2=0
с^2-12с+36-49-14с-с^2=0
-26с-13=0
-26с=13
с=2
a*b=7*7+24*0=49
IaI=V49+576=V625=25
IbI=V49+0=7
cos(a.b)=a*b/IaIIbI=49/25*7=7/25
tg(2П-а) = -tga