Expand the polynomial: (5a+1/5 b)^2

Expand the following:
(5 a + b/5)^2

(5 a + b/5) (5 a + b/5) = (5 a) (5 a) + (5 a) (b/5) + (b/5) (5 a) + (b/5) (b/5):
5×5 a a + (5 a b)/5 + (5 b a)/5 + (b b)/(5×5)

(5 a b)/5 = 5/5×a b = a b:
5×5 a a + a b + (5 b a)/5 + (b b)/(5×5)

(b×5 a)/5 = 5/5×b a = b a:
5×5 a a + a b + b a + (b b)/(5×5)

Combine powers. (b b)/(5×5) = (b^(1 + 1))/(5×5):
5×5 a a + a b + b a + (b^(1 + 1))/(5×5)

1 + 1 = 2:
5×5 a a + a b + b a + (b^2/5)/5

5 a×5 a = 5×5 a^2:
5×5 a^2 + a b + b a + (b^2/5)/5

5×5 = 25:
  25 a^2 + a b + b a + (b^2/5)/5

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Step-by-step explanation: