March 25, 2010

Solving Equations with Rational Expressions CA SS: 13.0

This lesson is the same as Chapter 3 Lesson 6, Clearing an Equation of Fractions or Decimals.

Multiply through by the lowest common denomiator.

p.453 (1-19:odd)

13 comments:

Anonymous said...

Phewww thanks for posting the homework I forgot to copy it down(: I'll finish it and report back if I have any questions!

Anonymous said...

how do u do #1 i dont get it..
3/8 + 4/5 = x/20????? i got 40 as the common denominator....help me!!

Anonymous said...

I tried number one but I can't get it right can someone help?

3/8 + 4/5= x/20

Then I found a common denominator and multiplied the fractions to get the denominators the same
3/8(5) + 4/5(8)= x/20

15/40 + 32/40= 47/40

Then I checked the answer which said 47/2 and I am confused how to get 47/2 PLEASE HELP(:

Anonymous said...

# 3 and 5 I did them and I ended up with the numerators and denominators switched can someone help me solve either 3 or 5 as an example for me so I can see where I made a mistake?
Thanks!

Natasha L Per.4 TA said...

num. 1

3/8 + 4/5 = x/20

40 is the least common denominator

40(3/8) + 40(4/5) = 40(x/20)
15 + 32 = 2x
47 = 2x
divide by two
x = 47/2

Natasha L Per.4 TA said...

umm Nicole what you are doing wrong is that you have to multiply the fractions with the lowest common denominator, such like the LCD is 40 in 3/8 4/5 x/20. When you multiply with the LCD you will be able to cancel out the denominator in the faction like so: 3/8 * 40/1 , the 8 cancels out leaving you with the answer 15.

Hosam I Per 3 said...

yah thats what i got

Anonymous said...

Thanks Natasha(:

JonathanF.per3 said...

Alright, I was going to ask about #5 but i see that's already answered.... 0.o

Hosam I Per 3 said...

I dont get #7 like i know how to get -1 but how did they get -4

Eric X. Per. 3 TA said...

Number 7:

x+4/x=-5
LCM=x, so multiply everything by x.
x(x+4/x)=x(-5)
x^2+4=-5x
+5x +5x
x^2+5x+4=0
Now you can factor the equation:
(x+1)(x+4)=0
x+1=0 x+4=0
-1 -1 -4 -4
x=-1 x=-4

So the two solutions are x={-1,-4}.

Anonymous said...

thank you natasha and eric
it helped me too (:
but im still abit confused on how you get the same denominator and "clear out" the fractions

Natasha L Per.4 said...

the "clearing out" is just cross canceling, or using the means extremes property.