1. The given series is
 4 â‹… 6 + 5 â‹… 7 + 6 â‹… 8 + ... + 4n( 4n + 2) = Â
For n=1
L.H.S=4.6=24
R.H.S=[4×5×15]÷6
   =300÷6
   =50
So, for n=1,
L.H.S≠R.H.S
Since the given expression is true for n=1 ,
So , the given series is untrue.
we should replace R.H.S by=4(n+1)(n+2)(4n-3)²
2.
12+42+72+.......+(3 n -2)2=
For n=1,
L.H.S=12
R.H.S=1×(6-3-1)/2
    =2/2
   =1
As L.H.S≠R.H.S
We should Replace R.H.S by [(3 n-1)(3 n-2)]2
3.The given sequence is
2+4+6+....+2n=n(n+1)
L.H.S
P(1)=2
R.H.S
1×(1+1)
=1×2
=2
( b) Â L.H.S
P(n)=2+4+6+.....2 k
This is an A.P having n terms.
tex]S_{n}=
       = n(n+ 1)
R.H.S=n(n+1)
So, P(k)=k(k+1)
(c) P(k+1)=2+4+6+.......+2(k+1)
This is an A.P having (k+1) terms.
       =(k+1)(k+2)
So, P(k+1)= (k+1)(k+2)
(Btw this is not my answer)