Question

If a + b = 10 and ab = 20 then the value of a3 + b3

is
1) 400
2) 470
3) 570​

Answer 1

Answer: 400

EXPLANATION :

Given,

=> a + b = 10

=> ab = 20

To find the value of a³ + b³

We know that,

a³ + b³ = (a + b)³ - 3ab (a + b)

Substitute the values

a³ + b³ = (10)³ - 3(20) [ 10 ]

= 1000 - 600

= 400

Therefore, the value of a³ + b³ is 400.

Answer 2

Given :

a+b = 10

ab = 20

To Find :

a³+b³

Solution :

a³+b³ = (a+b)³ -3ab(a+b)

Putting the values in the above expression :

a³+b³ = (10)³ -3(20)[10]

= 1000 -60(10) => 1000-600

= 400

The required value is 400.

Here we used the identity :

(a+b)³ = a³+b³+3ab(a+b)

=> à³+b³= (a+b)³-3ab(a+b)