if x⁴+y⁴+x²y²=21 and x²+y²-xy=7, then what is the value of  $${x\over y}+{y\over x}=?$$

If $$64^{x+1}={64\over 4^x}$$, then the value of x

If a, b are rational number and (a-1)√2+3=b√2+a, the value of (a+b) is : 

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 x = z = 225 and y = 226 then the value of : x³ + y³ + z³ – 3xyz is

If a + b = 1 and a³ + b³ + 3ab = k, then the value of k is

If (x + 6y) = 8, and xy = 2, where x > O, what is the value of (x³+216y³)?

What is the value of a²+b²+c²-2ab-2bc+2ca?