math symbol

y=2x^2-11x+(k+14)
有two real roots
find k
k is a positive integer
我用b^2-4ac
11^2-8(k+14)>0
呢到我就有problem
如果
121>8k+112
9/8>k

or
121-8k-112>0
9-8k>0
k>-9/-8
k>9/8

就係咁la，其實幾時要轉符號or unknown

p.s 幫手答 [present value of f.4 math]