derivative of s(t)= 1/(t+1)
We save the definition: s(t) = 1t + 1
To ease differentiation, the expression 1t + 1 is turned into (t + 1)-1
Let's perform the differentiation: ddt((t + 1)-1)
We differentiate using: ddt(fn) = n·ddt(f)·fn -1 (where f = t + 1)
ⓘ The derivative of x^n is n*x^(n-1): ddt((t + 1)-1) = -1·ddt(t + 1)·(t + 1)-2
-1·ddt(t + 1)·(t + 1)-2
ⓘ Multiplying by -1 gives the opposite: -1·ddt(t + 1)·(t + 1)-2 = -ddt(t + 1)·(t + 1)-2
-ddt(t + 1)·(t + 1)-2
ⓘ The factor is moved to the numerator or the denominator by changing the sign of its exponent, for a nonzero base: -ddt(t + 1)·(t + 1)-2 = -ddt(t + 1)(t + 1)2
-ddt(t + 1)(t + 1)2
ⓘ The derivative of a sum is the sum of the derivatives: ddt(t + 1) = 1 + 0
-1 + 0(t + 1)2
ⓘ Adding 0 changes nothing: 1 + 0 = 1
▶Derivative:   -1(t + 1)2