Join 60,000+ competitive exam aspirants
If x+x1=4, then x2+x21=?
12
18
14
16
14
If x+x1=k, then x2+x21=k2−2
x+x1=4
Squaring Both Sides
(x+x1)2=42x2+2⋅x⋅x1+x21=16x2+2+x21=16
Expanding using (a+b)2=a2+2ab+b2
Isolating x2+x21
x2+x21=16−2=14
x2+x21=14
C is correct — 14