If the direction ratio of two vectors are connected by the relations `a+b+c=0` and `a^2+b^2=c^2`. then the angle between two vectors

IF the direction ratios of two vectors are connected by the relations p + q + r = 0 and p^(2) + q^(2) - r^(2) = 0. Find the angle between them.

Direction ratios of two lines satisfy the relations 2a-b+2c=0 and ab+bc+ca=0 . Then the angle between two lines is

If the direction ratios of two lines are given by a + 2b + c = 0 and 11 bc +6ca - 14 ab = 0 . then the angle between these lines is

If a,b,c are unit vectors satisfying the relation a + b+sqrt(3) c = 0 , then the angle between a and b is

The non-zero vectors a, b and c are related as b = 5a and c = -2b. The angle between a and c is