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The equation for finding the angle between two vectors states that the dot product of the two vectors equals the product of the magnitudes of the vectors and the cosine of the angle between them.

Solve the equation for .

To find the dot product, find the sum of the products of corresponding components of the vectors.

Substitute the components of the vectors into the expression.

Simplify.

Remove parentheses.

Simplify each term.

Multiply by .

Multiply by .

Add and .

To find the magnitude of the vector, find the square root of the sum of the components of the vector squared.

Substitute the components of the vector into the expression.

Simplify.

Raise to the power of .

Raising to any positive power yields .

Add and .

Rewrite as .

Pull terms out from under the radical, assuming positive real numbers.

To find the magnitude of the vector, find the square root of the sum of the components of the vector squared.

Substitute the components of the vector into the expression.

Simplify.

Raising to any positive power yields .

Raise to the power of .

Add and .

Rewrite as .

Pull terms out from under the radical, assuming positive real numbers.

Substitute the values into the equation for the angle between the vectors.

Cancel the common factor of and .

Factor out of .

Cancel the common factors.

Factor out of .

Cancel the common factor.

Rewrite the expression.

Cancel the common factor of and .

Factor out of .

Cancel the common factors.

Factor out of .

Cancel the common factor.

Rewrite the expression.

Divide by .

The exact value of is .

Find the Angle Between the Vectors (5,0) , (0,9)