Processing math: 28%




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21.

If a,b,c are  distinct  real numbers are P,Q, R are three points  whose position  vectors are  respectively 

aˆi+bˆj+cˆk,bˆi+cˆj+aˆk and cˆi+aˆj+bˆk  , then QPR=


A) cos1(a+b+c)

B) π2

C) π3

D) cos1(a2+b2+c2abc)



22.

\cos \left(\frac{\pi}{7}\right)\cos \left(\frac{2\pi}{7}\right)\cos \left(\frac{4\pi}{7}\right)=


A) \frac{-1}{8}

B) \frac{1}{8}

C) -\frac{3\sqrt{3}}{8}

D) 1



23.

If   x=\frac{2.5}{3.6}-\frac{2.5.8}{3.6.9}\left(\frac{2}{5}\right)+\frac{2.5.8.11}{3.6.9.12}\left(\frac{2}{5}\right)^{2}-... \infty  then

7^{2}(12x+55)^{3}=


A) 3^{8}5^{3}

B) 3^{8}5^{5}

C) 3^{3}5^{5}

D) 3^{3}5^{8}



24.

The number of ways  in which four letters can be put in four addressed envelops so that no letter goes  into envelope  meant for it is


A) 8

B) 12

C) 16

D) 9



25.

If \alpha_{1},\alpha_{2},.......,\alpha_{n}  are the roots of x^{n}+px+q=0,  then (\alpha_{n}-\alpha_{1})(\alpha_{n}-\alpha_{2})...............(\alpha_{n}-\alpha_{n-1})=


A) n \alpha^{n-1}+q

B) \alpha_{1}^{2}+\alpha_{2}^{2}+.....+\alpha_{n-1}^{2}

C) \alpha_{n}^{n-1}+p

D) n\alpha_{n}^{n-1}+p



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