a + b = 5

<=> (a+b)3=125

 <=> a3 + 3a2b + 3ab2 + b3 = 125

<=> 3ab(a + b) + 35 = 125 (a3 + b3 = 35)

<=> 15ab = 90 (a + b = 5)

<=> ab = 6

a + b = 5

<=> (a + b)2 = 25

<=> a2 + 2ab + b2 = 25

<=> a2 + 12 + b2 = 25

<=> a2 + b2 = 13

a + b = 5

<=> \(\left(a+b\right)^3=125\) <=> a³ + 3a²b + 3ab² + b³ = 125

<=> 3ab(a + b) + 35 = 125 (a³ + b³ = 35)

<=> 15ab = 90 (a + b = 5)

<=> ab = 6

a + b = 5

<=> (a + b)² = 25

<=> a² + 2ab + b² = 25

<=> a² + 12 + b² = 25

<=> a² + b² = 13