Question

a plus b equal to 5 a square plus b square equal to 11 then prove that a cube plus b cube is equal to 20

Answer 1

Answer:

20

Step-by-step explanation:

Given that,  

a + b = 5

a square + b square = 11

We know,

(a + b ) ^2 = a square + b square + 2 ab

Thus putting the values,

(5)^2 = 11 + 2 ab

2 ab = 25 - 11

2 ab = 14

Thus,   ab = 7

Now we  know,

a cube + b cube = (a + b) (a square + b square - ab)

Thus putting the values from  above,

a cube + b cube = (5) (11 - 7)

                          = 5 * 4

                          = 20

Hence proved