Question

2. Find a3+b3
if a+b = 12 and ab =27.

Answer 1

Answer:

The answer is 756.............

Answer 2

Answer:

Given :-

a + b = 12

ab = 27

• To find :-

a³ + b³

• Salutation :-

[ Method - ( i ) ]

a³ + b³

= ( a + b )³ - 3ab ( a + b ) [ • Using identity ]

= ( 12 )³ - 3 × 27 × 12 [ • As given , ( a + b ) = 12 , ab = 27 ]

= 1728 - 972

= 756 [ • Required answer ]

Side note :-

• Used identity → ( a³ + b³ ) = ( a + b )³ - 3ab ( a + b )

___________________________

[ Method - ( ii ) ]

Let , a = 9 and b = 3

As , ( a + b ) = ( 9 + 3 ) = 12

And , ab = ( 9 × 3 ) = 27

Now ,

a³ + b³

= ( 9 )³ + ( 3 )³

= 729 + 27

= 756 [ • Required answer ]