F(x)=x^2+3 find and simplify f(t-5)
and f(a+h)-f(a) , f(a) - f(a-h)

1. (t-5)^2+3=t^2-10t+12+3=t^2-10t+15.

2. (a+h)^2+3=a^2+2ah+h^2+3
    (a^2)+3=a^2+3. Subtracting, we get h^2+2ah.

3. (a^2)+3=a^2+3
    (a-h)^2+3=a^2-2ah+h^2+3. Subtracting, we get 2ah-h^2.