If 0

consider the function f(x)=tan⁡x, defined on [a,b] such that a, b∈0,π2f′(c)=f(b)−f(a)b−a for some c∈(a,b)⇒sec2⁡C=tan⁡b−tan⁡ab−a⇒f(a,b)=sec2⁡C⇒f(a,b)>1 ∵sec2⁡C>1 as C∈(0,π/2)