數-代數 (9)-代數式b

√( k - 13 ) = √a + √a.........(1)
√k + √a = √( 2k + a - √k )............(2)
From(1):

√( k - 13 ) = √a + √a
√(k - 13) = √(4a)
k - 13 = 4a
k = 4a + 13......(3)
From (2):
k + a + 2√(ka) = 2k + a - √k
2√(ka) = k - √k
4ka = k^2 + k - 2k√k
4a = k + 1 - 2√k (Since k is not = 0,because√(0-13) )
sub (3) to it :
4a = (4a+13)+1 - 2√(4a+13)
0 = 14 - 2√(4a+13)
√(4a+13) = 7
4a+13 = 49
a = 9
k = 4*9 + 13
= 49