Q.Differentiate y=sin(3x2+2x) with respect to x.
Concept understanding — Chain Rule
The Chain Rule: Why It Makes Sense
Imagine you're assembling a toy. First you put part A into part B, then you put that combined piece into part C. The final toy's position depends on how you moved A, which then affected B, which then affected C. That's exactly what the chain rule captures — how a change in the first variable ripples through a sequence of functions to affect the final output.
Let's make this concrete. Suppose you have a function f that depends on g, and g itself depends on x:
y=f(g(x))
You want to know: if x changes by a tiny amount, how much does y change? The answer isn't just f′(g(x)) — because g(x) itself changes when x changes. You have to multiply the two rates:
- How fast does g change with respect to x? That's g′(x).
- How fast does f change with respect to its input g? That's f′(g(x)).
The total effect is the product:
dxdy=f′(g(x))⋅g′(x)
In Leibniz notation, this looks even more natural: dxdy=dudy⋅dxdu, where u=g(x). The du's "cancel" like fractions — though this is just a helpful memory aid, not a rigorous proof.
The Precise Statement
Chain Rule (single variable): If g is differentiable at x and f is differentiable at g(x), then the composite function h(x)=f(g(x)) is differentiable at x, and
h′(x)=f′(g(x))⋅g′(x)
That's it. One multiplication. But the power is enormous — it lets you differentiate almost any nested function.
A Simple Example
Differentiate h(x)=sin(3x2).
Here f(u)=sinu and g(x)=3x2. Then:
- f′(u)=cosu, so f′(g(x))=cos(3x2)
- g′(x)=6x
Multiply: h′(x)=cos(3x2)⋅6x=6xcos(3x2)
The most common mistake is forgetting to multiply by the inner derivative. Students often write dxdsin(3x2)=cos(3x2) and stop — that's wrong. The chain rule demands you also multiply by 6x.
Why It's Called a "Chain"
Think of a chain of links: x→g→f. Each link has its own rate of change. To find the total rate from x to f, you multiply the rates of each link. If you had three functions — say h(x)=f(g(k(x))) — you'd multiply three derivatives:
h′(x)=f′(g(k(x)))⋅g′(k(x))⋅k′(x)
The chain can be as long as you like. Each new function adds one more factor.
The Intuition in One Sentence
The chain rule says: the rate of change of the whole is the product of the rates of change of the parts, evaluated at the right places.
The chain rule is not optional — it's the backbone of calculus. Every derivative of a trigonometric, exponential, logarithmic, or power function that isn't just xn uses it. Master this, and you master differentiation.
The chain rule is one of the most heavily tested formulas in the NCERT Class 12 Continuity and Differentiability chapter, and it underlies nearly every differentiation problem in CBSE boards, JEE Main and JEE Advanced. Whether you're searching 'chain rule differentiation class 12 examples' or 'chain rule important questions for JEE', this f'(g(x))·g'(x) pattern is the formula every subsequent derivative rule in the syllabus builds on.
Outer function sin(⋅), inner function u=3x2+2x; apply the chain rule.
dxdy=(6x+2)cos(3x2+2x)
With u=3x2+2x so y=sinu, the chain rule (Section 3) gives dxdy=dudy⋅dxdu=cosu⋅dxdu. Since dxdu=6x+2,
dxdy=cos(3x2+2x)⋅(6x+2)=(6x+2)cos(3x2+2x).
dxdy=(6x+2)cos(3x2+2x)
Identify the outer function (sin) and inner function (3x2+2x); differentiate the outer function w.r.t. its own argument (giving cos(⋅)), keep the inner function unchanged inside it, then multiply by the derivative of the inner function.
Forgetting to multiply by the inner derivative (6x+2) entirely (writing just cos(3x2+2x)); differentiating sin(3x2+2x) as if it were sin(3x2)⋅sin(2x).
Showing the 12 most recent of 115 on this concept.
- CBSE 2026Set A1 markMCQQ.dxdx2+ax+1=(a) 2x2+ax+1x+a(b) 2x2+ax+12x+a(c) x2+ax+12x+a(d) 2x2+ax+11
›Reveal solutionSolution
dxdx2+ax+1=2x2+ax+12x+a.
Let u=x2+ax+1, so dxdu=2x+a.
Using dxdu=2u1⋅dxdu:
dxdx2+ax+1=2x2+ax+12x+a.
✓Final answer(b) 2x2+ax+12x+a.
- CBSE 2026Set A1 markMCQQ.dxd(sinx2)=(a) 2xcosx2(b) cosx2(c) x2cosx2(d) xcosx2
›Reveal solutionSolution
dxdsin(x2)=2xcos(x2).
Let u=x2, so dxdu=2x.
By the chain rule,
dxdsinu=cosu⋅dxdu=cos(x2)⋅2x=2xcos(x2).
✓Final answer(a) 2xcosx2.
- CBSE 2026Set A1 markMCQQ.dxdcotx=(a) 2cotx1(b) csc2x(c) 2cotx−csc2x(d) 2cotxcsc2x
›Reveal solutionSolution
dxdcotx=2cotx−csc2x.
Let u=cotx, so dxdu=−csc2x.
Using dxdu=2u1⋅dxdu:
dxdcotx=2cotx1⋅(−csc2x)=2cotx−csc2x.
✓Final answer(c) 2cotx−csc2x.
- CBSE 2026Set A1 markMCQQ.dxd(cosx)=(a) sinx(b) 2x−sinx(c) 2xsinx(d) 2x1
›Reveal solutionSolution
dxdcosx=2x−sinx.
Let u=x, so dxdu=2x1.
By the chain rule,
dxdcosu=−sinu⋅dxdu=−sinx⋅2x1=2x−sinx.
✓Final answer(b) 2x−sinx.
- CBSE 2026Set A1 markMCQQ.dxd(cosx3)=(a) −3x2sinx3(b) sinx3(c) 3x2sinx3(d) 3x2
›Reveal solutionSolution
Chain rule on cos(x3) gives −3x2sinx3.
Let the inner function be u=x3, so y=cosu.
dxdy=dudy⋅dxdu=(−sinu)(3x2)=−3x2sinx3.
✓Final answer(A) −3x2sinx3.
- CBSE 2026Set ANNUAL1 markMCQQ.Write the derivative of log(cosex).(a) −tanex(b) extanex(c) −extanex(d) tanex
›Reveal solutionSolution
Using the chain rule twice, dxdlog(cosex)=−extanex.
Let y=log(cosex). We differentiate using the chain rule, working from the outside in.
Step 1: Differentiate log(u) where u=cosex:
dxdy=cosex1⋅dxd(cosex)
Step 2: Differentiate cos(v) where v=ex:
dxd(cosex)=−sin(ex)⋅dxd(ex)=−sin(ex)⋅ex
Step 3: Combine:
dxdy=cosex−exsinex=−extanex
✓Final answerThe correct option is (c) −extanex.
- CBSE 2026Set ANNUAL1 markMCQQ.If y=cos−1(1+x21−x2), 0<x<1, then dxdy is equal to(a) 1+x21(b) 4+x2(c) 1+x22(d) x+x22
›Reveal solutionSolution
Put x=tanϕ so the expression simplifies to cos−1(cos2ϕ)=2ϕ=2tan−1x, whose derivative is standard.
Let x=tanϕ. Then 1+x21−x2=1+tan2ϕ1−tan2ϕ=cos2ϕ.
So y=cos−1(cos2ϕ)=2ϕ=2tan−1x (valid for 0<x<1, i.e. 0<ϕ<π/4, so 2ϕ is in the principal range).
dxdy=1+x22.
✓Final answerThe correct option is (c) 1+x22.
- CBSE 2026Set ANNUAL1 markQ.If y=ex+ex2+…+ex5, then find dxdy.
›Reveal solutionSolution
Differentiate each term exn using the chain rule: dxdexn=nxn−1exn.
y=ex+ex2+ex3+ex4+ex5
dxdy=ex+2xex2+3x2ex3+4x3ex4+5x4ex5.
✓Final answerdxdy=ex+2xex2+3x2ex3+4x3ex4+5x4ex5.
- CBSE 2026Set ANNUAL1 markMCQQ.dxd(cos3x)=(a) sin3x(b) −3sin3x(c) cos3x(d) −3cos3x
›Reveal solutionSolution
Differentiate cos(3x) using the chain rule: derivative of cosu is −sinu, times dxdu.
dxd(cos3x)=−sin(3x)⋅dxd(3x)=−sin(3x)⋅3=−3sin3x.
✓Final answer(b) −3sin3x.
- CBSE 2026Set ANNUAL1 markMCQQ.dxdtan−1(x2)=(a) 1+x42x(b) 1+x2x(c) 1+x2x3(d) None of these
›Reveal solutionSolution
Use dxdtan−1u=1+u21⋅dxdu with u=x2.
dxdtan−1(x2)=1+(x2)21⋅dxd(x2)=1+x42x.
✓Final answer(a) 1+x42x.
- CBSE 2026Set ANNUAL1 markMCQQ.dxdesinx=(a) esinx⋅cosx(b) esinx(c) cosx(d) None of these
›Reveal solutionSolution
Differentiate eu with u=sinx: derivative is eu⋅dxdu.
dxdesinx=esinx⋅dxd(sinx)=esinxcosx.
✓Final answer(a) esinx⋅cosx.
- CBSE 2026Set ANNUAL1 markMCQQ.dxd(logsecx)=(a) tanx(b) cotx(c) cscx(d) None of these
›Reveal solutionSolution
Differentiate log(secx) using dxdlogu=uu′ with u=secx.
dxdlog(secx)=secx1⋅dxd(secx)=secx1⋅secxtanx=tanx.
✓Final answer(a) tanx.
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.