Question

5. If a + 2b = 5; then show that : a3 + 863 + 30ab = 125. ​

Answer 1

Answer:

Given that a+2b=5;

We need to find a3  +8b3  +30ab

Now consider the cube of a+2b:

(a+2b)3  = a3 + (2b)3  + 3 × a × 2b × (2b+a)

(a+2b)3  = a3  + 8b3  + 6ab × (2b+a)

5 3  = a3   + 8b3  + 6ab × 5

125  3   = a3  + 8b3  + 30ab

Thus the value of a3  + 8b3 + 30ab = 125.

Answer 2

Answer:

SOLUTION

Given that a + 2b = 5 ;

We need to find a³ + 8b³ + 30ab: Now consider the cube of a + 2b :

( a + 2b)³ = a³ + (2b)³ + 3x a x 2b x (a+ 2b)

=a³ + 8b³ + 6ab x (a + 2b)

53 = a ^ 3 + 8b ^ 3 + 6ab * 5

[:a+2b=5]

125 = a ^ 3 + 8b ^ 3 + 30ab

Thus the value of a³ + 8b³ +

30ab is 125.

Explanation:

Given that a + 2b = 5 ;

We need to find a3 +8b3 +30ab

Now consider the cube of a+2b:

(a+2b)3 a3 + (2b)3 +3× a × 2b × (2b+a)

(a+2b)3 = a3 + 8b3 + 6ab × (2b+a)

53 a3 + 8b3 + 6ab x 5

125 = a3 + 8b3 + 30ab

Thus the value of a3 + 8b3 + 30ab = 125.

hope it helps u