Question

9x^2 + (p+20)xy + 49y^2 is a perfect square, what is the value of p

Answer 1

9x²+(p+20)xy+49y² is the square of 3x+7y

∴(p+20)xy=2*3x*7y
⇒p+20=42
∴p=22

i hope it helps!!

Answer 2

as it is perfect square middle term must be 2xy.
therefore 2×3x×7y=(p+20)xy
42=p+20
p=42-20
=22