Question Details

If  a   and  b  are two vectors such that | a | = 7  and | b | = 4 , then the value of scalar product of vectors  2 a 3 b  and  2 a + 3 b is

Options

A

52


B

25

C

340

D

430

Show Answer

Correct Answer :

Option A

52


Solution :

The correct option is 52.

To find the scalar product (dot product) of the vectors 2a3b and 2a+3b, we can use the distributive property of the scalar product (dot product), which is similar to the algebraic identity (xy)(x+y)=x2y2.

Let's write down the expression for the scalar product:
(2a3b)(2a+3b)

Expanding the dot product using the distributive property, we get:
(2a)(2a)+(2a)(3b)(3b)(2a)(3b)(3b)

Using the properties of the scalar product, specifically that uv=vu (commutativity) and uu=|u|2, we can simplify the expression:
4(aa)+6(ab)6(ba)9(bb)

Since ab=ba, the middle terms cancel out:
4|a|29|b|2

We are given that |a|=7 and |b|=4. Now, substitute these values into the simplified expression:
4(7)29(4)2

Calculate the squares:
4(49)9(16)

Multiply the terms:
196144

Perform the subtraction:
196144=52

Therefore, the value of the scalar product is 52.

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