Algebra and Applications Test 1

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Question : 38 of 40

Marks: +1, -0

If

x ^ 3 + y ^ 3 = 35

and

x + y = 5

, then the value of

1/x+1/y

will be :

$1 /3$
$5 / 6$
6
$2/3$

Solution:

x^3 + y^3 = 35

and

x + y = 5

We have an identity

(x + y)^3 = x^3 + y^3 + 3xy (x + y)

(5)^3 = 35 + 3xy (5)

125 = 35 + 15xy

90 = 15xy

xy=90/15=6

∴1/x+1/y={x+y}/{xy}=5/6

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