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15 Feb 2017, 03:34
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Difficulty:
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Question Stats:
79% (01:32) correct
21%
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based on 175
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Which of the following are solutions to the equation (625x^4−16)=0?
I. −2/5
II. 2/5
III. −4/25
A. I only
B. II only
C. I and II
D. II and III
E. I, II, and III
I. −2/5
II. 2/5
III. −4/25
A. I only
B. II only
C. I and II
D. II and III
E. I, II, and III
15 Feb 2017, 05:28
Kudos
Bookmarks
625x^4-16=0
(25x^2-4)*(25x^2+4)=0
so or (25x^2-4) =0 or (25x^2+4) =0 or both
second cant be 0 as 25x^2 can not equal = -4 as x^2 is always positive,
so (25x^2-4) =0
25x^2=4
X=2/5 or x=-2/5
answer is C
(25x^2-4)*(25x^2+4)=0
so or (25x^2-4) =0 or (25x^2+4) =0 or both
second cant be 0 as 25x^2 can not equal = -4 as x^2 is always positive,
so (25x^2-4) =0
25x^2=4
X=2/5 or x=-2/5
answer is C
15 Feb 2017, 06:20
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Bunuel
Which of the following are solutions to the equation (625x^4−16)=0?
I. −2/5
II. 2/5
III. −4/25
A. I only
B. II only
C. I and II
D. II and III
E. I, II, and III
I. −2/5
II. 2/5
III. −4/25
A. I only
B. II only
C. I and II
D. II and III
E. I, II, and III
Hi,
Two ways..
1) proper method..
\(625x^4-16=0......625x^4=16.....5^4*x^4=2^4.........(5x)^4=2^4\)..
Take 4th root..
5x=2....X=2/5 or
5x=-2...X=-2/5..
So only I and II..
2) substitution method..
since x is to EVEN power, x will have both POSITIVE and NEGATIVE value with same numeric value..
So if 2/5 is there , -2/5 will be there.. also all choices have ATLEAST one of them..
So we look for only -4/25..
Substitute and the value does not fit..
Only I and II
C
