Mathematics Multiple Choice Questions on “Derivatives”.
1. Find the derivative of ex2.
a) ex2
b) 2x
c) 2ex2
d) 2xex2
Answer: d
Clarification: We apply chain rule. First we differentiate x2.
(frac{d}{dx}) (x2) = 2x
Now, we know that (frac{d}{dx}) (ex) = ex
We differentiate ex2 in the same manner and then multiply with the derivative of x2
(frac{d}{dx}) (ex2) = 2xex2
2. What is the value of (frac{d}{dx}) (sin x tan x)?
a) sin x + tan x sec x
b) cos x + tan x sec x
c) sin x + tan x
d) sin x + tan x sec2x
Answer: a
Clarification: We follow product rule (frac{d}{dx}) (f.g) = g.(frac{d}{dx}) (f) + f.(frac{d}{dx}) (g)
Here, f = sin x and g = tan x
(frac{d}{dx}) (sin x tan x) = cos x tan x + sec2 x sinx
(frac{d}{dx}) (sin x tan x) = sin x + tan x sec x
3. What is the value of (frac{d}{dx}) (sin x3 cos x2)?
a) 3x2 cos x2 cos x3 + 2x sin x3 sin x2
b) 3x2 cos x2 cos x3 – 2x sin x3 sin x2
c) 2x cos x2 cos x3 – 2x sin x3 sin x2
d) 2x cos x2 cos x3 + 3x2 sin x3 sin x2
Answer: b
Clarification: We follow product rule(frac{d}{dx}) (f.g)= g.(frac{d}{dx}) (f)+ f.(frac{dy}{dx}) (g)
Here f = sin x3 and g = cos x2
(frac{d}{dx}) (f) = 3x2 cos x3
(frac{d}{dx}) (g) = -2x sin x2
We now substitute this in our main equation,
= cos x2.3x2 cos x3 + sin x3.(-2x sin x2)
= 3x2 cos x2 cos x3 – 2x sin x3 sin x2
4. What is the value of (frac{d}{dx}(frac{a^x}{e^x}))?
a) (frac{a^x (ln ,a-a^x)}{e^x})
b) (frac{a^x (ln, a-e^x)}{e^x})
c) (frac{a^x (ln, a-1)}{e^x})
d) (frac{a^x (ln, a-1)}{(e^x)(e^x)})
Answer: c
Clarification: Using quotient rule, we know that, (frac{d}{dx} (frac{f}{g}) = frac{g.frac{d}{dx} (f) – f.frac{d}{dx}(g)}{g^2})
Here, f = ax and g = ex
(frac{d}{dx} (frac{a^x}{e^x}) = frac{e^x.frac{d}{dx}(a^x)-a^x.frac{d}{dx}(e^x)}{(e^x)(e^x)})
(frac{d}{dx} (frac{a^x}{e^x}) = frac{e^x a^x ln, a-a^x e^x}{(e^x)(e^x)})
(frac{d}{dx} (frac{a^x}{e^x}) = frac{a^x (ln ,a-1)}{e^x})
5. What is the value of ln (frac{3}{x})?
a) (frac{2}{x^3})
b) (frac{-3}{x^3})
c) (frac{-9}{x^3})
d) (frac{9}{x^3})
Answer: c
Clarification: We use chain rule to find (frac{d}{dx})(ln (frac{3}{x})).
(frac{d}{dx}(ln frac{3}{x})) = (frac{1}{frac{3}{x}} frac{d}{dx}(frac{3}{x}))
(frac{d}{dx}(ln frac{3}{x})) = (frac{3}{x}(-frac{3}{x^2}))
(frac{d}{dx}(ln frac{3}{x})) = (frac{-9}{x^3})
6. The derivative of ln ex = 1. Is the statement true or false?
a) True
b) False
Answer: a
Clarification: We know that ln ex = x
(frac{d}{dx}) (x) = 1
7. What is the value of (frac{d}{dx})(ex sinx + ex cos x)?
a) 0
b) 2 cosx
c) 2ex.sin x
d) 2ex.cos x
Answer: d
Clarification: We need to use product rule in both the terms to get the answer.
(frac{d}{dx}) (f.g) = g.(frac{d}{dx}) (f)+ f.(frac{dy}{dx}) (g)
(frac{d}{dx}) (ex sin x + ex cos x) = (ex.(frac{d}{dx}) (sin x) + sin x.(frac{d}{dx}) (ex)) + (ex.(frac{d}{dx}) (cos x) + cos x.(frac{d}{dx}) (ex))
(frac{d}{dx}) (ex sin x + ex cos x) =(ex.cos x + sin x . ex) + (ex.(-sin x) + cos x.ex)
(frac{d}{dx}) (ex sin x + ex cos x) = ex.cos x + sin x . ex – ex.sin x + cos x.ex
(frac{d}{dx}) (ex sin x + ex cos x) = 2ex.cos x
8. What is the value of (frac{d}{dx}) (ex tan x) at x = 0?
a) 0
b) 1
c) -1
d) 2
Answer: b
Clarification: We need to use product rule in both the terms to get the answer.
(frac{d}{dx}) (f.g) = g.(frac{d}{dx}) (f)+ f.(frac{dy}{dx}) (g)
Here f = ex and g = tan x
(frac{d}{dx}) (ex tan x) = tan x.(frac{d}{dx}) (ex) + ex.(frac{d}{dx}) (tan x)
(frac{d}{dx}) (ex tan x) = tan x.ex + ex . sec2x
At x = 0 we get,
= tan 0.e0 + e0.sec20
= 0.(1) + 1.(1)
= 1
9. What is the value of (frac{d}{dx})(cos2 x tan x) at x = 1?
a) -1
b) 0
c) -2
d) 1
Answer: d
Clarification: We need to use product rule in both the terms to get the answer.
(frac{d}{dx}) (f.g) = g.(frac{d}{dx}) (f) + f.(frac{d}{dx}) (g)
Here f = cos2 x and g = tan x
To differentiate f, we need to use chain rule.
(frac{d}{dx}) (cos2 x tan x) = tan x.(frac{d}{dx}) (cos2 x) + cos2 x.(frac{d}{dx}) (tan x)
(frac{d}{dx}) (ex tanx) = tan x.(-2 cos x sin x) + cos2 x.sec2 x
At x = 1 we get,
= tan0.(-2 cos 0 sin 0) + cos2 0.sec2 0
= 1
10. What is the value of (frac{d}{dx}(frac{cosx}{secx ,tanx}))?
a) -tan2 x(3 sin2 x – cos2 x)
b) -cot2 x(3 sin2 x – cos2 x)
c) -cot2 x(3 sin2 x + cos2 x)
d) -tan2 x(3 sin2 x + cos2 x)
Answer: c
Clarification: (frac{d}{dx}(frac{cosx}{secx ,tanx}) = frac{d}{dx}(frac{cosx}{frac{1}{cosx}frac{sinx}{cosx}}))
=(frac{d}{dx}(frac{cos^3x}{sinx}))
Using quotient rule, we know that, (frac{d}{dx} (frac{f}{g}) = frac{g.frac{d}{dx} (f) – f.frac{d}{dx}(g)}{g^2})
Here, f = cos3 x and g = sin x
(frac{d}{dx}(frac{cos^3x}{sinx})) = (frac{sinx.frac{d}{dx} (cos^3x)-cos^3x.frac{d}{dx}(sinx)}{sin^2x})
(frac{d}{dx}(frac{cos^3x}{sinx})) = (frac{sinx (-3 cos^2 x ,sin x) – cos^3x(cosx)}{sin^2x})
(frac{d}{dx}(frac{cos^3x}{sinx})) = (frac{-3 sin^2x ,cos^2x – cos^4x}{sin^2x})
(frac{d}{dx}(frac{cos^3x}{sinx})) = -cot2 x(3 sin2 x + cos2 x)
11. What is the value of (frac{d}{dx}(frac{secx}{cosec, x ,tanx}))?
a) 0
b) 1
c) cos x
d) sin x
Answer: a
Clarification: (frac{d}{dx}(frac{secx}{cosec, x, tanx})) = (frac{d}{dx}(frac{{1} {cosx}}{frac{1}{sin, x}.frac{sinx}{cosx}}))
= (frac{d}{dx}) (1)
= 0
