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51.

If y = log x then y2 = (a) \(\frac{1}{x}\)(b) \(-\frac{1}{x^2}\)(c) \(-\frac{2}{x^2}\)(d) e2

Answer»

(b) \(-\frac{1}{x^2}\)

y = log x

∴ y1\(\frac{1}{x}\)

∴ y2\(\frac{-1}{x^2}\)

52.

Which of the following function is neither even nor odd? (a) f(x) = x3 + 5 (b) f(x) = x5 (c) f(x) = x10 (d) f(x) = x2

Answer»

(a) f(x) = x3 + 5

Since it has a constant term 5. 

f(x) = x3 + 5 

f(-x) = (-x)3 + 5 = -x3 + 5. 

It is not either f(x) or -f(x).

53.

If f(x) = x2 and g(x) = 2x + 1 then (fg)(0) is: (a) 0 (b) 2 (c) 1(d) 4

Answer»

(a) 0

(fg)(0) = f(0) g(0) 

= 02 (2(0) + 1) 

= 0(1) 

= 0

54.

If f(x) = 2x and g(x) = \(\frac{1}{2^x}\) then (fg)(x) is: (a) 1 (b) 0 (c) 4x (d) \(\frac{1}{4^x}\)

Answer»

(a) 1

(fg) x = f(x) g(x) = 2x \(\frac{1}{2^x}\) = 1

55.

If f(x) = ex and g(x) = loge x then find (i) (f + g) (1) (ii) (fg) (1) (iii) (3f) (1) (iv) (5g) (1)

Answer»

(i) (f + g) (1) = e1 + loge 1 = e + 0 = e 

(ii) (fg) (1) = f(1) g(1) = e1 loge1 = e x 0 = 0 

(iii) (3f) (1) = 3 f(1) = 3 e1 = 3e 

(iv) (5g) (1) = 5 (g) (1) = 5 loge= 5 x 0 = 0

56.

Solve: x3 + y3 = 3axy

Answer»

Given x3 + y3 = 3axy 

3x2 + 3y2\(\frac{dy}{dx}\) = 3a(x .\(\frac{dy}{dx}\) + y.1)

\(\frac{dy}{dx}\)(3y2 – 3ax) = 3ay – 3x2\(\frac{dy}{dx}\) 

\(\frac{ay - x^2}{y^2 - ax}\)