Plot[Sin[((x*π)/2)], {x, 0, 4}]

Plot[Sin[(π/2)], x]
?Plot

Simplify [(a^2) n + (a^2) (n^2) + 
        ban - (ban^2) + (b^2) n + 2  (b^2) + (b^2) (n^2) - 
        bn]

Solve [
      b*a*n - b*a*(n^2) - b*n + (a^2)* n + (a^2) *(n^2) + 
          (b^2) *(2 + n + (n^2)) == 0, b]

{{b -> (1/(2 (2 + n + (n^2))))(n - a n + 
              a (n^2) - (Sqrt[(((-n + a n - a (n^2)))^2) - 4 (2 + n + (n^2)) ((a^2) n + (a^2) (n^2))]))}, {b -> (1/(2 (2 + 
                    n + (n^2))))(n - a n + 
              a (n^2) + (Sqrt[(((-n + a n - a (n^2)))^2) - 4 (2 + n + (n^2)) ((a^2) n + (a^2) (n^2))]))}}

Solve[
      (b^2) + 2*a*
            b (( n - 1)/(n + 1)) - (((3 - n)*(a^2))/(1 + n)) == 0, b]

{{b -> -a}, {b -> ((3 a - a n)/(1 + n))}}
Simplify [
      n ((a^2) - (c^2)) = (((b - n*a - n*c))^2) - (b^2)]

Simplify [
      n ((a^2) - (c^2)) = (((b - n*a - n*c))^2) - (b^2)]

Simplify [-n ((a^2) - (c^2)) + (((b - n*a - n*c))^2) - 
          (b^2) == 0]

Solve[(a + c) n (-2 b + c + a (-1 + n) + 
              c n) == 0, c]