How does 3^ + 3^+1 = 3^ + 3×3?? Please help me!!

3^n + 3^{n+1} = 3^n + 3×3^n

When you have for example:   3²×3³ then you have:

(3×3)×(3×3×3) = 3×3×3×3×3 = 3⁵ which is  3²⁺³

It works with any exponents, so:

if  3²⁺³ = 3²×3³ then   3ⁿ⁺¹ = 3ⁿ×3¹ = 3ⁿ×3 = 3×3ⁿ

and so:

3ⁿ + 3ⁿ⁺¹ = 3ⁿ + 3×3ⁿ

a28=58

step-by-step explanation:

a1=a1+(n-1)d

a28= 4+ (28-1)2

a28=4+(27)(2)

a28=4+54

a28=58