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x is disible by 42.

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x is disible by 42.

by alexdallas » Sat Aug 15, 2009 3:39 pm
x is divisible by 42. Which of the following
numbers is definitely a factor of x2? (Choose
all that apply.)
a) 63 b) 33 c) 36 d) 8

ANSWER:
Answer: a) 63 and c) 36
If x definitely has 2, 3 and 7 as factors, then when we square
x, we know that x2 will have two 2s, two 3s and two 7s as
factors. 63 is 7 × 3 × 3, and 36 is 2 × 2 × 3 × 3. Using the
factor foundation rule, we can guarantee that all numbers that
solely use those factors are factors of x2. Both 63 and 36 use
only prime factors found in x2.

My question is: 8=2X2X2. doesnt 8 include 2X2? why isnt 8 a good answer?

thank you to whomever can help :)
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Re: x is disible by 42.

by tohellandback » Sat Aug 15, 2009 6:58 pm
alexdallas wrote:x is divisible by 42. Which of the following
numbers is definitely a factor of x2? (Choose
all that apply.)
a) 63 b) 33 c) 36 d) 8

ANSWER:
Answer: a) 63 and c) 36
If x definitely has 2, 3 and 7 as factors, then when we square
x, we know that x2 will have two 2s, two 3s and two 7s as
factors. 63 is 7 × 3 × 3, and 36 is 2 × 2 × 3 × 3. Using the
factor foundation rule, we can guarantee that all numbers that
solely use those factors are factors of x2. Both 63 and 36 use
only prime factors found in x2.

My question is: 8=2X2X2. doesnt 8 include 2X2? why isnt 8 a good answer?



thank you to whomever can help :)
X = 2 * 3 *7 *k (because 42 is a factor of x)
X^2= 2^2 * 3^2 *7^2*K^2
here you can only be sure of two 2's. for 8 2 be a factor of X^2, we need 3 2's. Now if k is even , you will get your 2.
but if k is odd
let's say 5
X^2= 2^2 * 3^2 *7^2* 5^2
you don't have your third 2. thats why 8 may be or may not be a factor
The powers of two are bloody impolite!!
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Master | Next Rank: 500 Posts
Posts: 108
Joined: Sun Mar 15, 2009 2:04 pm

by alexdallas » Sun Aug 16, 2009 11:19 am
got it baws. thanks.
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