Math Is Fun Forum

demha

Member

Registered: 2012-11-25

Posts: 195

Simplifying

Three of these I am not sure how to do, one of them I did my self and posted here just to make sure I got the right answer.

1. {3[SQRT(3)] + 7}[SQRT(3) - 5]

A -35
B -32
C 3[SQRT(3)] + 2
D -8[SQRT(3)] - 26
E 3[SQRT(3)] - 12
F 3[SQRT(9)] - 8[SQRT(3)] - 35

2. 4/[SQRT(5)]

A 4/[SQRT(5)]
B{4[SQRT(5)]}/25
C 4/25
D [SQRT(5)]/25
E {4[SQRT(5)]}/5
F 100/[SQRT(5)]

Answer: E

3. 4x/{2y[SQRT(7)]}

A{4x[SQRT(7)]}/14y
B 28x/14y
C 14x/y
D 4x/14y 
E [SQRT(14)}/14y
F 4x/y[SQRT(7)]

4. A weight hangs on a spring. The vibration period of that weight is the time in which it makes a complete cycle in motion. Suppose the relationship between the vibration period "T" (in seconds) and the weight "w" (in kilograms) is given by T = 2 pi SQRT(w / 200). Find the period T for a spring with a hanging weight of 2.0 kilograms.

A 0.3 seoconds
B 0.6 seconds
C 0.9 seconds
D 1.2 seconds
E 1.5 seconds
F 1.9 seconds

5. Suppose that the volume "V" (in cubic feet) of a blimp with radius "r" is given by V = 4/3 * pi * r^3. If the blimp has a volume of 10,000 cubic feet, find the approximate radius of the blimp.

A 13.98 feet
B 14.5 feet
C 62864.79 feet
D 5863.2 feet
E 29 feet
F 13.367

I am guessing of setting up the equation as:

10,000 = 4/3 x pi x r^3

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"The thing about quotes on the Internet is you cannot confirm their validity"
~Abraham Lincoln

SPARKS_CHAN

Member

Registered: 2014-12-05

Posts: 15

Re: Simplifying

2

4

5

demha

Member

Registered: 2012-11-25

Posts: 195

Re: Simplifying

For #3 I came up to {4x[SQRT(7)]}/14y  which is answer A. Is that the correct answer?

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"The thing about quotes on the Internet is you cannot confirm their validity"
~Abraham Lincoln

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Simplifying

Hi;

It is the answer that matches A so in that sense it is correct based on the choices that are given but it is obviously not in simplified form.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Simplifying

hi demha

Q1. {3[SQRT(3)] + 7}[SQRT(3) - 5]

If this was (a+b).(c+d) you'd have to multiply each term from the first bracket with each from the second:

= ac + ad + bc + bd.

If you do this with the question you'll get a term with root 3 x root 3 = 3, and other terms.  It should simplify to something of the form (p + q.root 3)

Q4.  This is just a substitute and evaluate.

Q5 Yes, do what you say.  To solve for 'r' you need to 'un-do' the formula ... divide by 4/3, and by pi, and then find the cube root of that.

Hope that helps,

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

demha

Member

Registered: 2012-11-25

Posts: 195

Re: Simplifying

For #1 I still don't understand how to do it. Do you think you could show an example with a similar problem?

For #5 I am getting the answer 'F.'

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"The thing about quotes on the Internet is you cannot confirm their validity"
~Abraham Lincoln

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Simplifying

hi Demha,

F is correct.

example

Hope that helps. 

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

demha

Member

Registered: 2012-11-25

Posts: 195

Re: Simplifying

{3[SQRT(3)] + 7}  [SQRT(3) - 5]

First Part:
(sqrt 3).3(sqrt 3) + 15 (sqrt 3) + 7 (sqrt 3) + 35

Second Part:
3 x 3 + 15 (sqrt 3) + 7 (sqrt 3) + 35

Third Part:
9 + 22(sqrt 3) + 35

Fourth Part:
22(sqrt 3) + 44

Is this right?

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"The thing about quotes on the Internet is you cannot confirm their validity"
~Abraham Lincoln

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Simplifying

hi demha,

That's the right idea.  But you have missed the minus sign on -5.

So the line

(sqrt 3).3(sqrt 3) + 15 (sqrt 3) + 7 (sqrt 3) + 35

has two sign errors.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

demha

Member

Registered: 2012-11-25

Posts: 195

Re: Simplifying

(sqrt 3).3(sqrt 3) - 15 (sqrt 3) + 7 (sqrt 3) - 35

3 x 3 - 15 (sqrt 3) + 7 (sqrt 3) - 35

9 - 8(sqrt 3) - 35

-8(sqrt 3) - 26

So the answer will be D?

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"The thing about quotes on the Internet is you cannot confirm their validity"
~Abraham Lincoln

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Simplifying

Yes, that's what I think.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

demha

Member

Registered: 2012-11-25

Posts: 195

Re: Simplifying

Awesome! Thanks everyone!

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"The thing about quotes on the Internet is you cannot confirm their validity"
~Abraham Lincoln