Powers and Roots Practice Test 3

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Question : 3 of 40

Marks: +1, -0

If

x + y = 1

, then the value of

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

is:

-2
1
2
3

Solution:

If

x + y= 1

, value of

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

If one value is x then

y = 1 - x

Put it in the given equation:

x ^3 + y ^3 + 3xy

=x^3+(1-x)^3+3x(1-x)

=x^3+1-x^3-3x(1-x)+3x(1-x)

=x^3+1-x^3-3x+3x^2+3x-3x^2=1

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