√2x + √50x = 12; √(1 - x) + √(4 + x) = 3

a) √2x + √50x = 12
b) √(1 - x) + √(4 + x) = 3
c) Rút gọn
A = √16 + 6√7 + √16 - √7
B = √6x - 1 + √3√2