In some SAT **circle problems** you cannot have even an idea from math diagram of how to solve the circle problems. It means that the information given in the math shape is not sufficient. In such case, drawing an additional line by your judgment may help you to solve math circle problems. Following is an example to illustrate you how an additional line is added to solve circle problems in geometry.

# **How to solve circle problems****:Example**

In the figure, C is a point on the circle whose centre is O and whose radius is r, and OACB is a rectangle. What is the length of diagonal?

(A) 2/3 r

(B) r

(C) r^{2}

(D) r^{2}/2 п

(E) 2 r^{2}/ п

**Solution**:

It is difficult to have an idea of diagonal *AB* with information given in the figure. So we draw line of radius *OC* (dotted line). We observe that *OC* and *AB* are diagonals of rectangle *OABC*. Since diagonal of a rectangle are always equal, so diagonal *AB* is equal to diagonal *OC*, which is radius **r** **(B)**.

See you need not to use circle formula or triangle formula or Pythagorean Theorem to calculate the radius of the circle in this circle problem.

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How to solve circle problems easily?

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This is another approach to solving circle geometry questions. great idea!