Question

If \[\vartriangle \left( x \right) = \left| {\begin{array}{*{20}{c}} 1&{\cos x}&{1 - \cos x} \\ {1 + \sin x}&{\cos x}&{1 + \sin x - \cos x} \\ {\sin x}&{\sin x}&1 \end{array}} \right|\]         then $$\int\limits_0^{\frac{\pi }{2}} {\vartriangle \left( x \right)dx} $$   is equal to

A. $$\frac{1}{4}$$
B. $$\frac{1}{2}$$
C. $$0$$
D. $$ - \frac{1}{2}$$  
Answer :   $$ - \frac{1}{2}$$
Solution :
\[{C_3} \to {C_3} + {C_2} - {C_1}\,\,{\text{gives }}\vartriangle \left( x \right) = \left| {\begin{array}{*{20}{c}} 1&{\cos x}&0 \\ {1 + \sin x}&{\cos x}&0 \\ {\sin x}&{\sin x}&1 \end{array}} \right| = \cos x - \cos x\left( {1 + \sin x} \right) = - \sin x \cdot \cos x\]
$$\therefore \,\,\int\limits_0^{\frac{\pi }{2}} {\vartriangle \left( x \right)dx = - \frac{1}{2}\int\limits_0^{\frac{\pi }{2}} {\sin 2x\,dx} } $$
\[\int\limits_0^{\frac{\pi }{2}} {\vartriangle \left( x \right)dx = - \frac{1}{2}\left[ { - \frac{{\cos 2x}}{2}} \right]_0^{\frac{\pi }{2}} = \frac{1}{4}\left( {\cos \pi - \cos 0} \right) = - \frac{1}{2}.} \]

Releted MCQ Question on
Algebra >> Matrices and Determinants

Releted Question 1

Consider the set $$A$$ of all determinants of order 3 with entries 0 or 1 only. Let $$B$$  be the subset of $$A$$ consisting of all determinants with value 1. Let $$C$$  be the subset of $$A$$ consisting of all determinants with value $$- 1.$$ Then

A. $$C$$ is empty
B. $$B$$  has as many elements as $$C$$
C. $$A = B \cup C$$
D. $$B$$  has twice as many elements as elements as $$C$$
Releted Question 2

If $$\omega \left( { \ne 1} \right)$$  is a cube root of unity, then
\[\left| {\begin{array}{*{20}{c}} 1&{1 + i + {\omega ^2}}&{{\omega ^2}}\\ {1 - i}&{ - 1}&{{\omega ^2} - 1}\\ { - i}&{ - i + \omega - 1}&{ - 1} \end{array}} \right|=\]

A. 0
B. 1
C. $$i$$
D. $$\omega $$
Releted Question 3

Let $$a, b, c$$  be the real numbers. Then following system of equations in $$x, y$$  and $$z$$
$$\frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} - \frac{{{z^2}}}{{{c^2}}} = 1,$$    $$\frac{{{x^2}}}{{{a^2}}} - \frac{{{y^2}}}{{{b^2}}} + \frac{{{z^2}}}{{{c^2}}} = 1,$$    $$ - \frac{{{x^2}}}{{{a^2}}} + \frac{{{y^2}}}{{{b^2}}} + \frac{{{z^2}}}{{{c^2}}} = 1$$     has

A. no solution
B. unique solution
C. infinitely many solutions
D. finitely many solutions
Releted Question 4

If $$A$$ and $$B$$ are square matrices of equal degree, then which one is correct among the followings?

A. $$A + B = B + A$$
B. $$A + B = A - B$$
C. $$A - B = B - A$$
D. $$AB=BA$$

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