It can't be.
say, theta= 0 degrees. then, putting the values, the answer is 19/2.
see? check the question again.
thats not actually 1 but 10
i'm sorry i can't give the exact proof to you, but in these type of questions, when i don't reach the answer by exact methods, i put in values. that won't be entirely wrong, at least in most cases. put cos theta equal to 1, then minus 1 s they are the two extreme values. hence, it satisfies the condition.
i found out by exact proof that the max value is less than 10 ( i got 15/2 to be exact) but don't know how to find out the minimum value.
i put in the formula, (a-b)^2 is less than or equal to a^2 + b^2