Question

已知2的X次方为3,4的Y次方为5,8的Z次方为7,求8的X-X-2Y的值

Answer 1

是8的X-Y-2Z次方吧?

2^x=3;4^y=2^2y=(2^y)*(2^y)=5得2^y=5/2;8^z=7可知

8^(x-y-2z)=8^x+1/8^y+1/8^(2z)

=2^(3x)+1/2^(3y)+1/(8^z+8^z)

=2^x+2^x+2^x+1/(2^y+2^y+2^y)+1/(8^z+8^z)

=3+3+3+2/(5+5+5）+1/(7+7)

=9+2/15+1/14