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If s=3ij and t=2i+3j, find \((t - 3s).(t + ...

If s=3ij and t=2i+3j, find (t3s).(t+3s).

A.

-77

B.

-71

C.

-53

D.

-41

Correct answer is A

s=3ij;t=2i+3j

t3s=(2i+3j)3(3ij)=2i+3j9i+3j=7i+6j

t+3s=(2i+3j)+3(3ij)=2i+3j+9i3j=11i

(t3s).(t+3s)=(7i+6j).(11i)=77