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Really basic substitution.. (1 Viewer)

Makro

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Its from a larger question, but I just failed at the subbing in to find the y value.

y = (3x - 1) (x - 2)^4.

x = 2/3, what do we do here? I kept getting 1/16 :/ correct answer 3/13/81

Thanks.
 

hermand

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make sure you use brackets for everything on your calculator, so it looks like this...
(3(2/3)-1)((2/3)-2)^(4)

then you get 3 13/81
 

Timothy.Siu

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Its from a larger question, but I just failed at the subbing in to find the y value.

y = (3x - 1) (x - 2)^4.

x = 2/3, what do we do here? I kept getting 1/16 :/ correct answer 3/13/81

Thanks.
sub in x=2/3

y=(3x(2/3)-1)(2/3-2)^4
=(-4/3)^4=256/81

u cud just use a calculator lol
 

Makro

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Hmm, I tried with my calculator at least twice to get the wrong answer, and now when I try I get it right. I was just sort of wondering what's the order of operations (if that's even the right term) to solving this. Just say that x=1. Do you simplify the first bracket then multiply by the next or something else.

Sorry for being a nuisance.
 

Timothy.Siu

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Hmm, I tried with my calculator at least twice to get the wrong answer, and now when I try I get it right. I was just sort of wondering what's the order of operations (if that's even the right term) to solving this. Just say that x=1. Do you simplify the first bracket then multiply by the next or something else.

Sorry for being a nuisance.
u can just type the whole thing in the calculator at once, just make sure u have brackets, so for x=1, just type

(3x1-1)(1-2)^4 and you'll get the correct answer
similarly, for the x=2/3, u shud type

(3x2/3-1)(2/3-2)^4

for that one u cud either use the divide sign or the fraction sign, but u have to be careful for the divide sign for some questions

also if ur worried about calculator work, u cud split it up and solve it in two turns,
so u cud go 3x2/3-1=1 and then do 2/3-2=-4/3 Ans^4=3 13/81 and then u multiply both parts together, 3 and 13/81 times 1=3 13/81
 

Xcelz

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Its from a larger question, but I just failed at the subbing in to find the y value.

y = (3x - 1) (x - 2)^4.

x = 2/3, what do we do here? I kept getting 1/16 :/ correct answer 3/13/81

Thanks.

Well here it a little note, (3 x 2/3) = 2 (since the denominator cancels the 3's out)

Therefore 2-1 = 1. So the first bracket is now equal to 1.

Now 2nd bracket, (2/3 - 2) = (-4/3)
Now to the power of 4.
=256/81

divide by 81. boom you have 3/13/81. be careful when you plug it into the calculator, use lots of brackets to sort things out.
 

Makro

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Ah right, I must have been making silly mistakes when I tried, was just making sure there wasn't something basic I was forgetting (besides logic) thanks again :)
 

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