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Show that x3 + y3 = (x + y )(x2 – xy + y2).
Solution: Since (x + y)3 = x3 + y3 + 3xy(x + y)
∴ x3 + y3 = [(x + y)3] –3xy(x + y)
= [(x + y)(x + y)2] – 3xy(x + y)
= (x + y)[(x + y)2 – 3xy]
= (x + y)[(x2 + y2 + 2xy) – 3xy]
= (x + y)[x2 + y2 – xy]
= (x + y)[x2 + y2 – xy]
Thus, x3 + y3 = (x + y)(x2 – xy + y2)
How?
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Show that x3 + y3 = (x + y )(x2 – xy + y2). Solution: Since (x + y)3 =...
Understanding the Identity
To prove the identity \( x^3 + y^3 = (x + y)(x^2 - xy + y^2) \), we can start with the expansion of \( (x + y)^3 \).

Step 1: Expand \( (x + y)^3 \)
- The expansion gives:
\[
(x + y)^3 = x^3 + y^3 + 3xy(x + y)
\]

Step 2: Rearranging the Equation
- From the expansion, we can isolate \( x^3 + y^3 \):
\[
x^3 + y^3 = (x + y)^3 - 3xy(x + y)
\]

Step 3: Factor Out \( (x + y) \)
- Notice that both terms on the right side contain \( (x + y) \):
\[
x^3 + y^3 = (x + y)((x + y)^2 - 3xy)
\]

Step 4: Simplifying \( (x + y)^2 - 3xy \)
- Now, we simplify \( (x + y)^2 - 3xy \):
\[
(x + y)^2 = x^2 + 2xy + y^2
\]
- Therefore:
\[
(x + y)^2 - 3xy = x^2 + 2xy + y^2 - 3xy = x^2 + y^2 - xy
\]

Final Result
- Substitute this back into the equation:
\[
x^3 + y^3 = (x + y)(x^2 + y^2 - xy)
\]
Hence, we have shown that:
\[
x^3 + y^3 = (x + y)(x^2 - xy + y^2)
\]
This completes the proof of the identity.
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Show that x3 + y3 = (x + y )(x2 – xy + y2). Solution: Since (x + y)3 = x3 + y3 + 3xy(x + y)∴ x3 + y3 = [(x + y)3] –3xy(x + y)= [(x + y)(x + y)2] – 3xy(x + y)= (x + y)[(x + y)2 – 3xy]= (x + y)[(x2 + y2 + 2xy) – 3xy]= (x + y)[x2 + y2 – xy]= (x + y)[x2 + y2 – xy]Thus, x3 + y3 = (x + y)(x2 – xy + y2) How?
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