Complex numbers  TOPIC_SOLVED

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Complex numbers

Postby Hannahred2 on Tue May 07, 2013 8:13 pm

Here's the problem: square root x-8 (all under square root) + square root x-7 (all under square root) =5. I know you have to subtract square root x-7 from the one side and do it to the side with the 5 too. I know you square both to remove the square root. When you foil, you get a lot of stuff, but here's the important part: do you get -x-7, -x+7, or x-7? Because when I foiled, I got square root x-7 -5 square root x-7. Since there is a neg sign before the 5's, do you distribute it to the whole thing, or just leave it as x-7?!


I used an algebra solver to find out what happens when you foil it. It said just x-7. Is that right? For my final answer, I got x=13.76 or 13 19/25
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Re: Complex numbers

Postby jg.allinsymbols on Tue May 07, 2013 9:36 pm

Hannahred2 wrote:Here's the problem: square root x-8 (all under square root) + square root x-7 (all under square root) =5. I know you have to subtract square root x-7 from the one side and do it to the side with the 5 too. I know you square both to remove the square root. When you foil, you get a lot of stuff, but here's the important part: do you get -x-7, -x+7, or x-7? Because when I foiled, I got square root x-7 -5 square root x-7. Since there is a neg sign before the 5's, do you distribute it to the whole thing, or just leave it as x-7?!


I used an algebra solver to find out what happens when you foil it. It said just x-7. Is that right? For my final answer, I got x=13.76 or 13 19/25



F.O.I.L. will give the same result as if you use distributive property. Working with the acronym, First, Outer, Inner, Last.


Let me use plain text:
(x-8)^0.5+(x-7)^0.5=5
(x-8)^.5=5-(x-7)^0.5
Now square both sides.
x-8=(5-(x-7)^0.5)^2
YOUR tricky part is what to do with the righthand side.
Using FOIL,
=5^2-5(x-7)^0.5-5(x-7)^0.5+(x-7)
=5^2-10(x-7)^0.5+x-7
=-10(x-7)^0.5+x+18
Current Summary, x-8=-10(x-7)^0.5+x+18
From that, you still want to isolate the square root expression and then square both sides, do other simplifications and solve for x.
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Re: Complex numbers

Postby Hannahred2 on Wed May 08, 2013 11:30 am

Why are you multiplying by (.5)? Where'd you get the number at?
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  TOPIC_SOLVED

Postby stapel_eliz on Wed May 08, 2013 11:34 am

Hannahred2 wrote:Why are you multiplying by (.5)? Where'd you get the number at?

He wasn't. He was raising to the one-half power, which is the same as taking the square root. :wink:
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