Question

is 90 a perfect square

Answer 1

Perfect Squares →

Perfect Squares are those numbers , which can be Expressed as the product of two numbers 'n' , i.e →

Let out Number be 'm'

m will be called as perfect square if m = n×n or n² , where n is an integer.
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Examples of perfect squares →

4 as it can be Expressed as 2×2 or, 2²

9 as it can also be Expressed as 3×3 or 3²
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To find out whether 90 is a perfect square of not , first we'll do prime Factorization of 90→

90 = 2 × 3 × 3 × 5

or, ✓90 = ✓(2×3×3×5)

[ Here , we don't have pair for 2 and 5 , so they'll be under surds while 3 has it's pair so we'll get 3 out.]

or, ✓90 = 3✓(2×5)

or, ✓90 = 3✓10

Hence , 90 is not an perfect square.
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Answer 2

No because 90 cannot be written in the form of product of two equal numbers so it is not a perfect square. For e.g. 81 can be written in the form 9×9 hence it is a perfect square.
THERE IS NOTHING MORE TO ELABORATE HERE EVEN IF YOU DON'T UNDERSTAND YOU CAN ASK ME AGAIN.