If | a |=3,| b |=5 and | c |=7 and a + b + c = 0 , then the angle between a and b is

Step-by-step solution

aligned & a + b + c =0 & a + b =- c & | a + b |^2=| c |^2 & | a |^2+| b |^2+2| a || b | =| c |^2 & 3^2+5^2+2 3 5 =7^2 & = 15 30 = 1 2 = 3 & = 3 aligned