Given:
f(x)=3x2
The derivative of a function f(x) is defined as:
f′(x)=limh→0f(x+h)−f(x)h
Putting f(x) in above expression, we get:
⇒f′(x)=limh→03(x+h)2−3x2h
⇒f′(x)=limh→03x2(3(x+h)2−x2−1)h
⇒f′(x)=limh→03x2(3(x+h)2−x2−1)(x+h)2−x2×(x+h)2−x2h
⇒f′(x)=limh→03x2(3(x+h)2−x2−1)(x+h)2−x2×2hx+h2h
⇒f′(x)=limh→03x2(3(x+h)2−x2−1)(x+h)2−x2×(2x+h)
[∵limx→0ax−1x=logea]
⇒f′(x)=3x2×loge3×(2x+0)
⇒f′(x)=2x(3x2)loge3
Therefore, the derivative of 3x2 is 2x(3x2)loge3