Question

3. If a + 2b = 10 and ab = 15, then find the value
of a3 + 8b3​

Answer 1

Step-by-step explanation:

Use the hint they gave you.... If

%28a%2B2b%29%5E3+=+a%5E3+%2B+8b%5E3+%2B+6ab%28a%2B2b%29 then the expression you are to evaluate is

a%5E3+%2B+8b%5E3+=+%28a%2B2b%29%5E3+-+6ab%28a%2B2b%29

You are given the values of both (a+2b) and (ab) -- plug them into that equation and evaluate.

Answer 2

Step-by-step explanation:

Given a +2b = 10 and ab = 15 Consider, a3 + 8b3 = a3 + (2b)3 = (a + 2b)3 − 3 × a × 2b(a + 2b) [Since, a3 + b3 = (a + b)− 3ab(a + b)] = (a + 2b)3 − 6ab(a + 2b) = (10)3 − 6 × 15 × 10 = 1000 − 900 = 100