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26.

The common roots of the equations $z^{3}+2z^{3}+2z+1=0$   and $z^{2018}+z^{2017}+1=0$ satisfy  the equation


A) $z^{2}-z+1=0$

B) $z^{4}+z^{2}+1=0$

C) $z^{6}+z^{3}+1=0$

D) $z^{12}+z^{6}-1=0$



27.

If x=a  ,y=b,z=c is the solutions of the system of simultaneous linear equations x+y+z=4 , x-y+z=2 , x+2y+2z=1 , then ab+bc+ca=


A) 0

B) -25

C) 1

D) -4



28.

If $\triangle_{1}=\begin{bmatrix}1 & a^{2}&a^{3}\\1 & b^{2}&b^{3}\\1&c^{2} &c^{3} \end{bmatrix} and \triangle_{2}=\begin{bmatrix}bc & b+c&1 \\ca & c+a&1\\ab&a+b&1 \end{bmatrix}$

 then   $\frac{\triangle_{1}}{\triangle_{2}}=$


A) ab+bc+ca

B) abc

C) 2(ab+bc+ca)

D) $(a+b+c)^{2}$



29.

For all positive integers  k, if the greatest divisor of $25^{k}+12k-1$  is d , then 4$\sqrt{d}$=


A) 36

B) 8

C) 20

D) 24



30.
 Let   $x\neq0, |x|<\frac{1}{2}$  and 
$ f(x)= 1+2x+4x^{2}+8x^{3}+....$  Then  $f^{-1}(x)= $ 

A) $\frac{x-1}{2x}$

B) $\frac{x-1}{2}$

C) $\frac{x-1}{x}$

D) $1-2x$



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