Question

4 Evaluate
(A+B).(A−B)
if
A=2i−3j+5k
and
B=3i+j−2k
20
22
24
26

Answer 1

Answer on Question #56111 – Math – Vector Calculus

4 Evaluate (A+B).(A-B) if A=2i-3j+5k and B=3i+j-2k

20

22

24

26

Solution

(A+B).(A-B)=(2i-3j+5k+3i+j-2k).(2i-3j+5k-3i-j+2k)=(5i-2j+3k)(-i-4j+7k)=5·(-1) i .i + (-2)(-4) j .j +3*7k.k =5·(-1)+(-2)(-4)+3·7=-5+8+21=24.

Answer: 24.

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