So for question 11, you have a = 6 and c = 12:
teacher comments:
Make sure that you always STATE the final answer... if you end up wth c2 = 4... then c=2 which is the SQRT of 4. Since 4 is a perfect square, you can give it's actual sqrt. IF you were to get something like c2 = 5... your answer would just be c=√5. Since 5 is NOT a perfect square, just leave the answer as a sqrt
Also... make sure that you understand when you SQUARE a SQRT... the operations CANCEL each other out and leave ONLY the number from under the radical!
Ex... √5 2 = √5 * √5 = 5
ex 2.... (2√5)2 = 2*2*√5*√5 = 4*5 = 20