Find It Out

Level 2

If $a+b=69$

$a^2+b^2=2525$

$a^3+b^3=?$

1 solution

Vaibhav Kandwal
Jan 14, 2015

Very Simple, we have $a+b=69$ , squaring on both sides.

$a^2 + b^2 + 2ab = 4761$ but $a^2 + b^2 = 2525$

so $2525 + 2ab = 4761$

or simply $ab=1118$ .

Now, $a^3 + b^3 = (a+b)(a^2+b^2-ab)$

Putting the values, we get

$\boxed{a^3+b^3=97083}$

I think the last equation should be a^3 + b^3 = (a + b)(a^2 + b^2 -ab)

Sean De Guzman - 6 years, 4 months ago

My bad, corrected..

Vaibhav Kandwal - 6 years, 4 months ago

Yup #Vaibhav You Are Right

Karan Ahire - 6 years, 5 months ago