You find the variable x or y in one of the lines of the problem and then substitute the value of the variable you first found into the other line of the problem to find the other variable. Then, you plug all of the values you found into either line/equation of the problem to ensure that one side of the equation you pick is equal to what is on the other side of the "=" symbol.
The simplified expression is
and the restriction is 
<h3>How to simplify the expression?</h3>
The expression is given as:

Express x^2 - y^2 as (x + y)(x - y) and factorize other expressions

Rewrite the expression as products

Cancel out the common factors

Express 4x^2 - y^2 as (2x - y)(2x + y)

Cancel out the common factors

Take the LCM

Hence, the simplified expression is
and the restriction is 
Read more about expressions at:
brainly.com/question/723406
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3^6 power. it would be 3 to the 6th power
Answer:
No
Step-by-step explanation:
An irrational number is a number that never ends or repeats. This decimal ends and it doesn't repeat.
Answer:
D
Step-by-step explanation:
It's these shapes because:
Rectangle- A quadrilateral with 2 pairs of congruent sides and only 90° angles is a rectangle.
Parallelogram- A quadrilateral with 2 pairs of parallel sides is a parallelogram.