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Vector Algebra

Question
CBSEENMA12034077

Find the angle between two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top such that open vertical bar straight a with rightwards arrow on top close vertical bar space equals space open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 and straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1.

Solution

Here open vertical bar straight a with rightwards arrow on top close vertical bar = open vertical bar straight b with rightwards arrow on top close vertical bar space equals space 3 comma space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 1
Let straight theta be the angle between straight a with rightwards arrow on top space and space straight b with rightwards arrow on top.
Now,
           straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space ab space cos space straight theta space space space space space space space space space space space space space space space rightwards double arrow space space space space 1 space equals space left parenthesis 3 right parenthesis thin space left parenthesis 3 right parenthesis space cos space straight theta
rightwards double arrow space space space cos space straight theta space equals space 1 over 9 space space space space space space space space space space space space space space space space rightwards double arrow space space straight theta space equals space cos to the power of negative 1 end exponent open parentheses 1 over 9 close parentheses