Question

a³+b³ and a³-b³ formulas

Answer 1

Answer:

i) a³+b³ = (a+b)(a²-ab+b²)

Or

= (a+b)³-3ab(a+b)

ii) a³-b³ = (a-b)(a²+ab+b²)

Or

= (a-b)³+3ab(a-b)

Explanation:

i) We know the algebraic identity:

a³+3a²b+3ab²+b³ = (a+b)³

=> a³+b³+3ab(a+b)=(a+b)³

=> a³+b³ = (a+b)³-3ab(a+b)---(1)

= (a+b)[(a+b)²-3ab]

= (a+b)(a²+2ab+b²-3ab)

= (a+b)(a²-ab+b²) ----(2)

Now ,

ii) By algebraic identity:

a³-3a²b+3ab²-b³ = (a-b)³

b)³=> a³-b³-3ab(a-b)=(a-b)³

b)³=> a³-b³ = (a-b)³+3ab(a-b)---(3)

)= (a-b)[(a-b)²+3ab]

3ab]= (a-b)(a²-2ab+b²+3ab)

3ab)= (a-b)(a²+ab+b²) ----(4)

Therefore,

i)a³+b³ = (a+b)(a²-ab+b²)

Or

= (a+b)³-3ab(a+b)

ii) a³-b³ =(a-b)(a²+ab+b²)

Or

= (a-b)³+3ab(a-b)

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