Question

Help please 
Найти угол между двумя прямыми 
5x-y+7=0 и 2x-3y+1=0

Answer 1

5x-y+7=0    2x-3y+1=0    α=?
y=5x+7       y=(2/3)x+1/3
tgα=(2/3-5)/(1+5*(2/3))=(-4¹/₃)/(1+5*(2/3)=(-13/3)/(1+10/3)=(-13/3)/(13/3)=-1 
α₁=3π/4=135°
α₂=7π/4=315°.