show that |a x b|^2 + |a.b|^2 = |a|^2 |b|^2. the "x" is supposed to mean cross product and the "." is dot product

User Icon for oobleck oobleck answered
3 years ago

|axb| = |a| |b| sinθ

a.b = |a| |b| cosθ
now square and add them up

User Icon for anon anon answered
3 years ago

thanks!!

User Icon for Explain Bot Explain Bot answered
11 months ago

To show that |a x b|^2 + |a . b|^2 = |a|^2 |b|^2, where "x" represents the cross product and "." represents the dot product, we can use the properties of vector algebra and the definitions of the cross product and dot product.

First, let's start with the left side of the equation:

|a x b|^2 + |a . b|^2

The cross product of two vectors, a and b, can be defined as:

|a x b| = |a| |b| sin(theta)

where |a| and |b| are the magnitudes of vectors a and b, and theta is the angle between the two vectors.

The dot product of two vectors, a and b, can be defined as:

|a . b| = |a| |b| cos(theta)

where |a| and |b| are the magnitudes of vectors a and b, and theta is the angle between the two vectors.

Now, let's substitute these values into the left side of the equation:

|a x b|^2 + |a . b|^2
= (|a| |b| sin(theta))^2 + (|a| |b| cos(theta))^2

Expanding and simplifying this expression, we get:

= |a|^2 |b|^2 sin^2(theta) + |a|^2 |b|^2 cos^2(theta)

Using the trigonometric identity sin^2(theta) + cos^2(theta) = 1, we can rewrite the above expression as:

= |a|^2 |b|^2 (sin^2(theta) + cos^2(theta))

Now, sin^2(theta) + cos^2(theta) equals 1, so we have:

= |a|^2 |b|^2 (1)

Since anything multiplied by 1 is equal to itself, we can simplify the expression further:

= |a|^2 |b|^2

This is the same as the right side of the equation.

Therefore, we have shown that |a x b|^2 + |a . b|^2 = |a|^2 |b|^2.