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 x = a - b, y = b - c, z = c - a, then the numerical value of the algebraic expression x³ +y³ + z³ -3xyz will be 

$$ {x^{8}+4\over{x^{4}+2x^{2}+2}}$$ is equal to

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

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

What is the compound interest on a sum of ₹25,000 after three years at a rate of 12 per cent per annum interest compounded yearly?  

If 15x² – 26x + 8 = (Ax + B) (Cx + D), where A and C are positive integers, then what is the value of (2A + B – C – 2D) ?

If $$ {a={1+x\over 2-x}}$$, then find the value $$ {1\over {a+1}}+{2a+1\over{a^{2}-1}}$$ ?