If x^4+x^3+x^2+x+1 = 0, then the value of x^{25} is

Find the value of (2-\sqrt{5} )^{198}\cdot (9+4\sqrt{5} )^{99}

Show that 81^7-27^9-9^{13} is divisible by 45

If a , b , c are real numbers such that 3^{a+b-c}7^{2b+c}5^{2a-b+c}=27 , find the value of a , b, c