Question

prove that |a•b|² = a²b²-(a•b)²​

Answer 1

Answer:

a x b= a b sin∅ .n, where a=lal and b=lbl (а х b)² = a² b² sin² (n)² = a² b² sin²∅ a²b²( 1-cos²∅)=a² b² - a² b² cos²∅ lal² lbl² -(a.b)² (∵ (n)²= 1).