If x²+4y²=17 and xy=2, where x>0,y>0, then what is the value of x³+8y³?

If $$ {x+{9\over x}=6}$$  then find the value of $$ {x^{2}+{1\over x^{3}}}$$

If $$ ({x+y\over z})=2$$ , then what is the value of $$ [{ {y\over {y-z}}}] +[{ {x\over {x-z}}}]$$.

if a+b+c=7 and a³+b³+c³-3abc=175, then what is the value of (ab+bc+ca)?

If $$ {a^4+1}={{a^2}\over{b^2}}{(4b^2-b^4-1)}$$,then what is the value of $${a^4+b^4}$$?

If $$ {(x-5)^{2} +{(y-2)^{2}}+{(z-9)^{2}=0}}$$ then what is the value of (x+y-z)?

If $$ {x^{4}+x^{2}y^{2}+y^{4}={21\over256}}$$ and $$ {x^{2}+xy+y^{2}={3\over16}}$$ then $$ {2(x^{2}+y^{2})}=?$$

 If $${\sqrt{7-2}\over\sqrt{7+2}}=a\sqrt{7}+b$$, then the value of a is :