4. As shown in Figure 5.111 to the right if the two small semicircles, each of radius 1 unit
with centres O' and O'' are contained in the
bigger semi-circle with center O, So that
O', O and O" are on the same line, then
what is the area of the shaded part?

Area of the shaded part is 3.14 square unit.

Step-by-step explanation:

Area of the shaded part = Area of large semicircle - (Area of two small semi circles)

Area of large semicircle with center O =

                                                                =

                                                                = 2π

Area of semicircle with center O' =

                                                      =

Area of semicircle with center O" =

Now substitute these values in the formula,

Area of shaded part =

                                  =

                                  = 3.14 square unit

Area of the shaded part is 3.14 square unit.

2. angles qrt and qst both measures 156 degrees.

step-by-step explanation:  

we have been given a diagram of a circle and we are told that measure of arc qvt is 156 degrees.  

we can see from our given diagram that angle qrt and angle qst subtends to arc qvt.

since we know that angles subtended by the same arc at the circumference are always equal.

by angle subtended by same arc theorem, measure of angle qrt and angle qst will be equal to the measure of arc qvt.

therefore, angles qrt and qst both measures 156 degrees and 2nd statement is the correct choice.