For what value of #k# is #x^2-21x+k# a perfect square trinomial?
1 Answer
Mar 26, 2017
Explanation:
Suppose:
#x^2-21x+k = (x+e)^2#
#color(white)(x^2-21x+k) = x^2+2ex+e^2#
Equating coefficients, we have:
#2e=-21#
So:
#e = -21/2#
and
#k = e^2 = (-21/2)^2 = 441/4 = 110.25#