If $x^2+y^2 = 45 $ and x - y = 5 then what is the value of $x^3 - y^3$ ?
Answer & explanation
Correct answer: option 4
If $x^2+y^2 = 45 $
x - y = 5
then what is the value of $x^3 - y^3$
x2 + y2 = 45
x - y = 5
We know that,
(a - b)2 = a2 + b2 - 2ab
a3 - b3 = (a - b)(a2 + b2 + ab)
So,x - y = 5
= (x - y)2 = 25
= x2 + y2 – 2xy = 25
= 45 – 2xy = 25
= 2xy = 20
= xy = 10
x3 - y3 = (x - y)(x2 + y2 + xy)
= 5{45 + 10}
= 5 × 55 = 275