Resolve into factor..
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9x^4 + 2x²y² + y^4

Arrange the terms

9x^4  + y^4 + 2x²y²

making the first two terms into a² + b²

(3x²)² + (y²)²   + 2x²y²

use the formula of a² + b² = (a+b)² - 2ab

(3x² + y²)²  - 2.3x².y²   + 2x²y²

(3x² + y²)²  - 6x²y² + 2x²y²

(3x² + y²)² - 4x²y²

(3x² + y²)² - (2xy)²

use the formula a² - b²

(3x² + 2xy + y²) (3x² - 2xy + y²)

Step-by-step explanation:

it means that the length is 5 times the width