Answer:
r=18 or r= -4
Step-by-step explanation:
Please see attached picture for full solution.
Before completing the square, ensure that the coefficient of r^2 is 1 and bring all the terms to the left hand side. In this case, we do not have to do this as it is already done.
Since the sign before '14r' is a negative sign, use the formula as shown in the first picture.
We know that the value of 'b' in the formula is 7 because 2(r)(b)= 14r. Hence,
2b= 14
b= 7
Step 5: remember to add '±' whenever you introduce a square root.