Question

Determine all values of k that make each of the following a perfect square trinomial. X^2+8x+k

Answer 1

Answer:

k can either be

12

or

−

12

.

Step-by-step explanation:

Consider the equation

0=x2+4x+4

. We can solve this by factoring as a perfect square trinomial, so

0=(x+2)2→x=−2 and−2

. Hence, there will be two identical solutions.

The discriminant of the quadratic equation (b2−4ac) can be used to determine the number and the type of solutions. Since a quadratic equations roots are in fact its x intercepts, and a perfect square trinomial will have

2 equal, or 1

distinct solution, the vertex lies on the x axis. We can set the discriminant to 0 and solve:

k2−(4×1×36)=0

k2−144=0

(k+12)(k−12)=0

k=±12