Triangle formed by three lines whose direction ratios are −1,1,1,1,2,0,1,1,0 is

Suppose that the given lines form a triangle ABC  Hence, cosA=−1+21+1+11+2=2−13cosB=1+21+21+1=2+16cosC=−1+11+11+1+1=0            Since cosC=0,the measure one angle in the triangle is right angle, so that the triangle formed by the given lines is right angled triangle.