Evaluate: 3C2
We know that
nCr=n!r!n-r!
Given, 3C2
Where n=3,r=2
∴nCr=n!r!n-r!=3!2!3-2!=3!2!1!but1!=1=3!2!×1=3×2×12×1×1=31=3
Hence, the value of3C2 is 3.
Evaluate If a + b + c = 15 and a2+b2+c2 = 125 , find ab + bc + ca