Help with rational expressions plz

**ohiostatefan** · July 19th 2009, 04:27 PM

If anybody could help, I have a math exam tomorrow, and I'm working on the review...but I've been having alot of trouble. Usually I can figure this stuff out by studying my notes...but I'm at a loss. Any help would be appreciated. The first three are problems that I don't understand, the rest are ones that I've completed, but I'm not sure if they're right.

1. $x^2+x=20$

2. Solve by quadratic formula:

$2x^2-5x=2$

3. Solve by completing the square:

$x^2+8x-9=0$

And the ones that I've completed, but not sure if they're right...I would appreciate if you could check these out.

1. $6y \sqrt{27x^3y} - 3x \sqrt{12xy^3} + xy \sqrt{4xy}$

I got:

$12xy \sqrt{3xy} + 2xy \sqrt{xy}$

2. $(4 \sqrt{x} + 3 \sqrt{y})(2 \sqrt{x} - 5 \sqrt{y})$

I got:

$8x-14 \sqrt{xy} - 15y$

3. $\frac{\sqrt 75a^8b^5}{\sqrt 5ab^2}$

I got:

$b \sqrt{15a^7b}$

**pickslides** · July 19th 2009, 05:03 PM

Originally Posted by ohiostatefan

1. $x^2+x=20$

$x^2+x-20=0$

factors of 20 that add to give 1 are -4 & -5 so

$(x-4)(x+5)$

Originally Posted by ohiostatefan

2. Solve by quadratic formula:

$2x^2-5x=2$

$2x^2-5x-2=0$

$x = \frac{-b\pm \sqrt{b^2-4ac}}{2a}$

in your case $a = 2, b= -5$ and $c = -2$

Originally Posted by ohiostatefan

3. Solve by completing the square:

$x^2+8x-9=0$

$(x^2+8x+16)-9-16=0$

$(x+4)^2-9-16=0$

$(x+4)^2-25=0$

the square is now complete, now solve!

**pickslides** · July 19th 2009, 05:09 PM

Originally Posted by ohiostatefan

If
And the ones that I've completed, but not sure if they're right...I would appreciate if you could check these out.

1. $6y \sqrt{27x^3y} - 3x \sqrt{12xy^3} + xy \sqrt{4xy}$

I got:

$12xy \sqrt{3xy} + 2xy \sqrt{xy}$

2. $(4 \sqrt{x} + 3 \sqrt{y})(2 \sqrt{x} - 5 \sqrt{y})$

I got:

$8x-14 \sqrt{xy} - 15y$

3. $\frac{\sqrt 75a^8b^5}{\sqrt 5ab^2}$

I got:

$b \sqrt{15a^7b}$

I agree with all your answers except the last problem, should be $\sqrt{15}a^7b^3$

**Stroodle** · July 19th 2009, 05:29 PM

Would you not be required to express the answer in its simplest form?

i.e. $a^3 b\sqrt{15ab}$

Thanks

*edit - Actually is the question supposed to be $\frac{\sqrt{75}a^8b^5}{\sqrt{5}ab^2}$ ? Because then the answer would be $a^7b^3\sqrt{15}$ . The above would be the answer to $\frac{\sqrt{75a^8b^5}}{\sqrt{5ab^2}}$ . As it's written the question looks like $\frac{\sqrt{7}\times 5a^8b^5}{\sqrt{5}ab^2}$ which $=a^7b^3\sqrt{35}$ .

Thread: Help with rational expressions plz

LinkBack

Thread Tools

Display

Help with rational expressions plz

Similar Math Help Forum Discussions

Rational Expressions

Rational Expressions

Rational Expressions and Radical Expressions

Rational expressions

Rational Expressions- NEED HELP PLZ

Search Tags