Using the identity (x+y)2+(x−y)2=2(x2+y2)
Compute the value of 42+22
15
10
20
18
The given expression is
42+22
=(3+1)2+(3−1)2
=2(32+12) [(x+y)2+(x−y)2=2(x2+y2)]
=2(9+1)
=2×10
=20