If a2 + b2 + c2 = 16, x2 + y2 + z2 = 25 and ax + by + cz = 20, then the value of  is
C.
The value of x which satisfies the equationÂ
is
(a2 + b2 + c2)
- (a2Â + b2Â + c2)
(a2 + 2b2 + c2)
(a2 + 2b2 + c2)
If x4 + 2x3 + ax2 + bx + 9 is a perfect square, where a and b are positive real numbers, then the values of a and b are
a = 5, b = 6
a = 6, b = 7
a = 7, b = 6
a = 7, b = 6