Perfect Square Trinomial

**Alienis Back** · September 30th 2008, 04:23 AM

Find two values of b that will make [tex]9x^2+bx+25[tex] a perfect square trinomial.

The formulas for Perfect Square Trinomial are:
[tex](a+b)^2=a^2+2ab+b^2[tex]
[tex](a-b)^2=a^2-2ab+b^2[tex]

As I solved:

[tex]9x^2+bx+25[tex]
[tex](3x)^2+2(3x)(5)+5^2[tex]
[tex]9x^2+6x(5)+25[tex]
[tex]9x^2+30x+25[tex]

Then...according to this one of those two values would be 30 but I'm not sure about it for I didn't find anything. I just replaced the given values [tex]9x^2[tex] and [tex]25[tex] into the middle term of the formula. And I couldn't find the other number.

**mr fantastic** · September 30th 2008, 04:27 AM

Originally Posted by Alienis Back

Find two values of b that will make [tex]9x^2+bx+25[tex] a perfect square trinomial.

The formulas for Perfect Square Trinomial are:
[tex](a+b)^2=a^2+2ab+b^2[tex]
[tex](a-b)^2=a^2-2ab+b^2[tex]

As I solved:

[tex]9x^2+bx+25[tex]
[tex](3x)^2+2(3x)(5)+5^2[tex]
[tex]9x^2+6x(5)+25[tex]
[tex]9x^2+30x+25[tex]

Then...according to this one of those two values would be 30 but I'm not sure about it for I didn't find anything. I just replaced the given values [tex]9x^2[tex] and [tex]25[tex] into the middle term of the formula. And I couldn't find the other number.

(3x + 5)^2 = ...... So b = 30 is correct.

(3x - 5)^2 = ..... So b = .......

**Alienis Back** · September 30th 2008, 04:29 AM

Why didn't it show the problem without the tags...mmm...I mean this "[tex]" things. I'd like to learn how to write problems using them. Is there any thread on the subject?

**mr fantastic** · September 30th 2008, 04:31 AM

Originally Posted by Alienis Back

Why didn't it show the problem without the tags...mmm...I mean this "[tex]" things. I'd like to learn how to write problems using them. Is there any thread on the subject?

$(a+b)^2=a^2+2ab+b^2$
$(a-b)^2=a^2-2ab+b^2$

come from [tex](a+b)^2=a^2+2ab+b^2[/tex] and [tex](a-b)^2=a^2-2ab+b^2[/tex].

See http://www.mathhelpforum.com/math-help/latex-help/

**Alienis Back** · September 30th 2008, 04:39 AM

Find two values of b that will make $9x^2+bx+25$ a perfect square trinomial.

The formulas for Perfect Square Trinomial are:
$(a+b)^2=a^2+2ab+b^2$
$(a-b)^2=a^2-2ab+b^2$

As I solved:

$9x^2+bx+25$
$(3x)^2+2(3x)(5)+5^2$
$9x^2+6x(5)+25$
$9x^2+30x+25$

Then...according to this one of those two values would be 30 but I'm not sure about it for I didn't find anything. I just replaced the given values $9x^2$ and $25$ into the middle term of the formula. And I couldn't find the other number.

**Alienis Back** · September 30th 2008, 04:40 AM

WOW...That's Great!!

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