Question 536075: Which values of b will make the expression x^2 + bx+400 a perfect square trinomial?
a. -80,80 b.-40,40 c.-100,100 d.-20,20
my wrong choice was d. which is the answer...? thx!
Found 2 solutions by algebrahouse.com, april4869:
Answer by algebrahouse.com(1659)   (Show Source):
You can put this solution on YOUR website! "Which values of b will make the expression x^2 + bx+400 a perfect square trinomial?"
a. -80,80 b.-40,40 c.-100,100 d.-20,20
B. is the answer
x² + 40x + 400
= (x + 20)(x + 20) {when factored}
or (x - 20)(x - 20)
For more help from me, visit: www.algebrahouse.com
Answer by april4869(19)  (Show Source):
You can put this solution on YOUR website! x^2 + bx + 400 will be a perfect square if b = 40. That is since 400 = 20^2, then b must be 2*20.
This follows the standard form (x + a)^2 = x^2 + 2ax + a^2
So the answer is 40.. and you can insert 40 into the equation to check. Rule of thumb, if you are unsure about multiple choice questions like this..just plug in each answer to see which one works! Sometimes it's the easiest way:)
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