Question

find the value of c that makes each trinomial a perfect square: x^2-21x+c.
I think it's Prime.

Answer 1

x^2-(42/2)x+((-42)^2)
c=(-42)^2

Answer 2

Please can you show me the steps

Answer 3

maybe I put it this way
x^2-21x+c =(x+a)^2
x^2-21x+c =x^2 +2a +a^2
compare both sides,
2a =-21
a=-21/2

c=a^2
=(-21/2)^2

Sorry that I have made a mistake in my first answer

Answer 4

Thank you so much