# Plus Two Maths Chapter Wise Previous Questions Chapter 5 Continuity and Differentiability

Kerala State Board New Syllabus Plus Two Maths Chapter Wise Previous Questions and Answers Chapter 5 Continuity and Differentiability.

## Kerala Plus Two Maths Chapter Wise Previous Questions Chapter 5 Continuity and Differentiability

### Plus Two Maths Continuity and Differentiability 3 Marks Important Questions

Question 1.
Consider $$f(x)=\left\{\begin{array}{ll} \frac{x^{2}-x-6}{x+2}, & x \neq-2 \\ -5, & x=-2 \end{array}\right.$$

(i) Find f(-2)
(ii) Check whether the function f(x) is continuous at x= -2. (March – 2009)

Question 2.
If f(x) = sin(Log x), prove that x2 y2 + xy1 + y = 0 (May -2009)
Given; y sin(Iogx)
Differentiating with respect to X;
$$y_{1}=\cos (\log x) \frac{1}{x} \Rightarrow x y_{1}=\cos (\log x)$$
Again differentiating with respect to x
$$\begin{array}{l} \Rightarrow x y_{2}+y_{1}=-\sin (\log x) \frac{1}{x} \\ \Rightarrow x^{2} y_{2}+x y_{1}=-y \Rightarrow x^{2} y_{2}+x y_{1}+y=0 \end{array}$$

Question 3.
(i) Establish that g(x) =1 – x + |x| is continuous at origin.
(ii) Check whether h(x) = |l – x + |x|| is continuous at origin. (March – 2010)
(i) Given; g(x) = 1 – x + |x| ⇒ g(x) (1 – x) + |x|
Here g(x) is the sum of two functions continuous functions hence continuous.
(ii) We have;
$$\begin{array}{l} f o g(x)=f(g(x)) \\ =\quad f(1-x+|x|)=|1-x+| x \mid=h(x) \end{array}$$
The composition of two continuous functions is again continuous. Therefore h(x) continuous.

Question 4.
Find $$\frac{d y}{d x}$$ of the following
$$\begin{array}{l} \text { (i) } x=\sqrt{a^{\sin ^{4} 4}} \quad y=\sqrt{a^{\cos ^{-1} t}} \\ \text { (ii) } y=\cos ^{-1} \frac{\left(1-x^{2}\right)}{\left(1+x^{2}\right)}, 0<x<1 \\ \text { (iii) } y=\sin ^{-1} 2 x \sqrt{1-x^{2}}, y_{\sqrt{2}}<x<y_{\sqrt{2}} \end{array}$$

Question 5.
Find $$\frac{d y}{d x} \text { if } x^{3}+2 x^{2} y+3 x y^{2}+4 y^{3}=5$$ (March – 2015)

Question 6.
Find all points of discontinuity of f where f is defined by $$f(x)=\left\{\begin{array}{ll} 2 x+3, & x \leq 2 \\ 2 x-3, & x>2 \end{array}\right.$$ (March – 2016)
In both the intervals x $$\leq[latex] 2 and x > 2 the function f(x) is a polynomial so continuous. So we havetocheckthe continuity at x = 2. Question 7. If ex-y = xy, then prove that [latex]\frac{d y}{d x}=\frac{\log x}{[\log \operatorname{ex}]}$$ (May – 2014; March – 2016)

### Plus Two Maths Continuity and Differentiability 4 Marks Important Questions

Question 1.
Find $$\frac{d y}{d x}$$ of the following (March – 2009)
$$\begin{array}{l} \text { (i) } y=\sin ^{-1}\left(3 x-4 x^{3}\right)+\cos ^{-1}\left(4 x^{3}-3 x\right) \\ \text { (ii) } y=\tan ^{-1}\left(\sqrt{\frac{1-\cos x}{1+\cos x}}\right) \end{array}$$

Question 2.
Consider the function f(x) = |x| x ∈ R
(i) Draw the graph of f(x) =|x|
(ii) Show that the function is continuous at x = 0. (March – 2010)

f(0) f(0) = 0. therefore continuous at x = 0.
AIso from the figure we can see that the graph does not have a break or jump.

Question 3.
(i) Find the derivative of y = xa + ax with respect to x.
(ii) If ey (x + 1) = 1 , showthat $$\frac{d^{2} y}{d x^{2}}=\left(\frac{d y}{d x}\right)^{2}$$ (May – 2011)

Question 4.
(i) Check the continuity of the function given by f(x) $$f(x)=\left\{\begin{array}{ll} x \sin \frac{1}{x}, & x \neq 0 \\ 1, & x=0 \end{array}\right.$$

(ii) Verify Mean Value Theorem for the function f(x) = x + 1/x in the interval [1,3]. (May – 2011)

Hence Mean Value Theorem ¡s verified.

Question 5.
(i) Determine the value of k so that the function (May – 2012)

Question 6.
Consider a fUnction f: R → R defined by
$$f(x)=\left\{\begin{array}{cc} a+x, & x \leq 2 \\ b-x, & x>2 \end{array}\right.$$

(i) Find a relation between a and b if f is continuous at x = 2.
(ii) Find a and b, if f is continuous at x2 and a + b = 2. (May – 2013)
(i) Since fis continuous at x = 2, we have;

(ii) Given a = 2 …(2) Solving (1) and (2) we have;
⇒ 2a = – 2 ⇒ a = – 1
⇒ b = 2 – a = 2 + 1 = 3

Question 7.
(i) Find if x = a(t – sin t) y = a(1 + cos t)
(ii) Verify Rolles theorem for the function f(x) = x2 + 2 in the interval [-2, 2] (March – 2014)

Question 8.
(a) Find the relationship between a and b so that the function f defined by
$$f(x)=\left\{\begin{array}{ll} a x^{2}-1, & x \leq 2 \\ b x+3, & x>2 \end{array}\right.$$ is continuous.

(b) Verify mean value theorem for the function f(x) = x2 – 4x -3 ¡n the interval [1, 4]. (May – 2014)
(a) Since fis continuous

Hence mean value theorem satisfies for the funcion.

Question 9.
(a) Find ‘a’ and ‘b’ if the function
$$f(x)=\left\{\begin{array}{ll} \frac{\sin x}{x}, & -2 \leq x \leq 0 \\ a \times 2^{x}, & 0 \leq x \leq 1 \\ b+x, & 1<x \leq 2 \end{array}\right.$$ is continous on [-2, 2]

(b) How many of the functions
f(x) = |x|, g(x) = |x|2, h(x) = |x|3 are not differentiable at x = 0?
(i) 0
(ii) 1
(iii) 2
(iv) 3 (March – 2015)
(a) Since f(x) is continuous on [-2, 2]

Question 10.
(a) Find the relation between ‘a’ and ‘b’ if the function f defined by
$$f(x)=\left\{\begin{array}{l} a x+1, x \leq 3 \\ b x+3, x>3 \end{array}\right.$$ is continuous.
lbx+3.x>3
(b) If e(x + 1) = 1, show thats $$\frac{d^{2} y}{d x^{2}}=\left(\frac{d y}{d x}\right)^{2}$$ (May -2015)

Question 11.
Find the value of a and b such that the function $$f(x)=\left\{\begin{array}{cc} 5 a & x \leq 0 \\ a \sin x+\cos x & 0<x<\frac{\pi}{2} \\ b-\frac{\pi}{2} & x \geq \frac{\pi}{2} \end{array}\right.$$ is continuous. (March – 2010)

Question 12.
(i) Find $$\frac{d y}{d x}, \text { if } x=a \cos ^{2} \theta ; y=b \sin ^{2} \theta$$
(ii) Find the second derivative of the function y = ex sinx. (May – 2017)

Question 13.
Find $$\frac{d y}{d x}$$ of the following (4 score each)
(i) yx = xy (May – 2015)
(ii) (COSx)y = (cosy)x (March – 2017)

### Plus Two Maths Continuity and Differentiability 6 Marks Important Questions

Question 1.
Find $$\frac{d y}{d x}$$ if
(i) sinx + cosy = xy
(ii) x = acos3t, y = asin3t
(iii) y = xx + (logx)x (May -2009; May -2011; March -2015)
(i) Given; sinx + cosy = xy
Differentiating with respect to x;

Question 2.
(i) Let y =3 cos(log x) + 4 sin (log x)
(a) Find $$\frac{d y}{d x}$$
(b) Prove that x2 y2 + xy1 + y = 0

(ii) (a) Find the derivative of y = e2x+logx
(b) Find $$\frac{d y}{d x}$$
if x = a (θ – sinθ), y = a(1 – cosθ) (March – 2009)

Question 3.
(i) Show that the function f (x) defined by f(x) = sin (cosx) is a continuous function.
(ii) If $$\frac{d y}{d x}=\frac{1}{\frac{d x}{d y}}$$, Show that $$\frac{d^{2} y}{d x^{2}}=\frac{-\frac{d^{2} x}{d y^{2}}}{\left(\frac{d x}{d y}\right)^{3}}$$ (May -2010)
Given; f(x) = sin(cos x)
Let g(x) = sin(x) and h(x) = cos x
Both these function are trigonometric functions hence continuous.
goh(x) = g(h(x)) = g(cos x) = sin(cos x) = f(x)

Since f(x) is the composition of two continuous functions, hence continuous.

Question 4.
(i) Let y = xsin x + (sinx)x. Find $$\frac{d y}{d x}$$
(ii) Given; $$y=\sqrt{\tan ^{-1} x}$$
(a) $$2\left(1+x^{2}\right) y \frac{d y}{d x}=1$$
(b) $$\left(1+x^{2}\right) y \frac{d^{2} y}{d x^{2}}+\left(1+x^{2}\right)\left(\frac{d y}{d x}\right)^{2}+2 x y \frac{d y}{d x}=0$$ (May – 2010; Onam – 2017)

Question 5.
(i) The function $$f(x)=\left\{\begin{array}{ll} 5, & x \leq 2 \\ a x+b, 2< & x<10 \text { is } \\ 21, & x \geq 10 \end{array}\right.$$ continuous. Find a and b
(ii) Find $$\frac{d y}{d x}$$ (a) if y = Sin (xsinx)
(iii) If y = ae” + be’; show that $$\frac{d^{2} y}{d x^{2}}-(m+n) \frac{d y}{d x}+m n y=0$$ (March – 2011)

Question 6.
(i) Match the following.

(ii) If y = sin-1 x, prove that (1 – x2) y2 – xy1 = 0 (March – 2012; May -2017)
(i) Consider $$f(x)=\left\{\begin{array}{ll} 3 x-8, & x \leq 5 \\ 2 k, & x>5 \end{array}\right.$$ Find the value of k if f(x) is continuous at x = 5.
(ii) Find $$\frac{d y}{d x}, \text { if } y=(\sin x)^{\log x}, \sin x>0$$
(iii) If y = (sin-1 x)2, then show that $$\left(1-x^{2}\right) \frac{d^{2} y}{d x^{2}}-x \frac{d y}{d x}=2$$. (March -2013)