If xy(x+y)=1, then $$ {1\over x^3 y^3}-{x^3-y^3}$$ is equal to-

$$ {a^2-b^2-2bc-c^2}\over{a^2+b^2+2ab-c^2}$$ is equal to

P and Q are center of two circles with radii 9 cm and 2 cm respectively, where PQ = 17 cm, R is the center of another circle of radius x cm, which touches each of the above two circles externally. If ∠PRQ = 90 °, then the value of x is 

What is the length of the radius of the circumcircle of the equilateral triangle, the length of whose side is 6√3 cm?

Inside a square ABCD, triangle BEC is an equilateral triangle. If CE and BD intersect at O, then ∠BOC is equal to?

A can complete a piece of work in 18 days, B in 20 days and C in 30 days. B and C together start the work and are forced to leave after 2 days. The time taken by A alone to complete the remaining work is?

Given that ( 1² +2²+3²+………..+10²)=385, the value of (2²+4²+6²+……20²) is equal to

If the circumradius of an equilateral triangle ABC be 8 cm, then the height of the triangle is