Question

if x+y=10 and xy=21 then evaluate x^3+y^3​

Answer 1

$\bf{Given,}$

$\rm{x + y = 10}$

$\rm{xy = 21}$

$\bf{use \: formula \: \rightarrow\: {(x + y)}^{3} = {x}^{3} + {y}^{3} + 3xy(x + y)}$

$\rm{ {10}^{3} = { x}^{3} + {y}^{3} + 3(21)(10) }$

$\rm{ {1000 = { x}^{3} + {y}^{3} + 630 }}$

$\rm{ { { x}^{3} + {y}^{3} = 1000 - 630 }}$

$\fbox {\rm{ { { x}^{3} + {y}^{3} = 370 }}}$

Answer 2

Answer: given,

X+y=10

XY=21

=x^3+y^3 to be founded

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

10^3 = x^3+x^3 + 63 (10)

1000=x^3+y^3+630

1000-630=x^3 +y^3

370=x^3+y^3(answer)

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