Question

(x-y)^3= (x^3=y^3-3xy(______)


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Answer 1

Answer:

answer is (21)

Step-by-step explanation:

X^3 + y^3 + 3xy = ?

x + y = 3

x y = 1

x + y = 3, x =3 – y , ( 3-y) y = 1, 3y – y^2 = 1 , y^2 – 3y +1 = 0

(y^2 – 3y + 9/4) - 9/4 + 1 = 0, y^2 – 3y + 9/4 = 5/4 , (y - 3/2 )^2 = 5/4 , y - 3/2 = 5/4

y = (3+√5)/2

X + ((3+√5)/2) = 3 , X= (3-√5)/2

( (3-√5)/2)^3 + ((3+√5)/2)^ 3 + 3( (3-√5)/2 X (3+√5)/2 ) = ?

9 - 4√5 + 9 + 4√5 + 3 (1) = 21