Question

What value of B makes the expression. x² + Bx + 81 a perfect square trinomial?

Answer 1

Answer:

B. 18

Step-by-step explanation:

$\text{Use}\ (a+b)^2=a^2+2ab+b^2\\\\\text{We have}\ x^2+Bx+81.\\\\\underbrace{x^2+Bx+9^2}_{a^2+2ab+b^2}\to Bx=2(9)x\\\\Bx=18x\to B=18$

Answer 2

Answer:

B.) 18

Step-by-step explanation:

To find the correct b value we use this formula

b² - 4ac = 0

b = What we are solving for

a = 1

c = 81

b² - 4(1)(81) = 0

b² - 324 = 0

b² = 324

$b = \sqrt{324}$

b = ±18

And 18 is one of the answer choices

So B.) 18 is the correct answer.