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1 mark

If x
3
=184+y
3
and x=4+y, then the value of (x+y) is (given that x>0 and y>0):

  1. A
    −2
    11

  2. B
    2
    14

  3. C
    −2
    14

  4. D
    2
    11

Solution & Step-by-step Explanation

Given equations:
x
3
−y
3
=184

x−y=4

We know the algebraic identity:

x
3
−y
3
=(x−y)(x
2
+xy+y
2
)
184=4(x
2
+xy+y
2
)
x
2
+xy+y
2
=46
We can express x
2
+xy+y
2
as:

x
2
+xy+y
2
=(x−y)
2
+3xy
46=(4)
2
+3xy
46=16+3xy
3xy=30⟹xy=10
Now we need to find the value of (x+y). We use the identity:

(x+y)
2
=(x−y)
2
+4xy
(x+y)
2
=4
2
+4(10)
(x+y)
2
=16+40=56
x+y=±
56


=±2
14



Since it is given that x>0 and y>0, their sum (x+y) must be positive.

x+y=2
14

Practice this question

Try it yourself before checking the explanation above.

If x
3
=184+y
3
and x=4+y, then the value of (x+y) is (given that x>0 and y>0):
A
−2
11

B
2
14

C
−2
14

D
2
11

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